[dbux-practice] Get dbux-projects ready for real-world practicing purposes

# re-design dbux-practice list
* [x] #603
* [x] Introduce exercises: show `stepsToReproduce` in an intuitive and meaningful way (currently available for `todomvc`)
* make sure, there is a button to review them, as well
* consider showing them directly in the `PracticeSession` view?
* [ ] render user timer results somehow in `ExerciseNode` - if they solved it, did they time it? How long did it take?
* [ ] maybe even summaries per chapter?
* [x] render project-related information in `ExerciseNode`
* (because in chapter view, the parent node is not the `ProjectNode` anymore)
* -> added project name to `description`
* [x] rename `bug` (and `experiment`) to `exercise` (continual WIP)

# Misc
* [x] when failing to tag a bug line, render some buttons in the notification
* "That sucks!"
* "Help" (does the same as "That Sucks!" iirc)
* [x] add progress indicators(icon and description) to each ChapterNode`
* [x] Can we have `BaseGroupNode` `Expanded` by default (see `BaseGroupNode.constructor`)?
* does the constructor argument simply not work?
* if it does not work, add [reveal](https://code.visualstudio.com/api/references/vscode-api#2220) ([related discussion here](https://github.com/microsoft/vscode/issues/55879)) API into our `BaseTreeViewNode{,Provider}` (at least add a `BaseTreeViewNode.reveal` method)
* [ ] visually differentiate between buggy and non-buggy exercise (with and without `bugLocations`)
* or: `bug` and `exploration` (non-buggy)
* [x] during `switchToExercise` (and related functions), make sure, all files inside the project folder are closed
* -> else, there might be a chance that the user sees the patch applied before their eyes
* [ ] add `previous` and `next` exercise buttons, so one can quickly move between them
* [ ] When finishing a task, show a final `modal` that summarizes the results and shows the previous/next button
* consider `codesignal` + `leetcode`
* [ ] allow user to review and reset all their own changes they have made for each `exercise`
* Add new button `review my changes`.
* When clicked, show a modal similar to the existing `Show diff in new tab and cancel`.
* But instead of "ignore" add a "reset" option (with `confirm` modal)
* [ ] #615

# More Complex Tasks

* [ ] explain why there is no leaderboard, even with a timer
* [ ] improve help menu
* also add a button for a visual cheatsheet?
* [ ] more user configuration when running things
* [ ] allow easily toggling all Dbux debug output via configuration (Domi)
* [ ] add buttons to UI to change the config (Michael)
* [ ] re-enable and fix `tutorial` + introduction system
* [ ] add some type of clean-up operation for every bug
* -> e.g. in `todomvc`, if the stored data in `localStorage` is corrupted, the next experiment will also be affected
* -> easiest solution: produce an "initial `localStorage`" state when switching to each exercise
* The project has a default `async resetExercise(exercise)` function, which can be overwritten or otherwise customized by each exercise.
* NOTE: this might be annoying since the user might get a feeling that they lose their data, but its probably not quite worth trying to keep the user state for each exercise
* [x] change the "reset progress" button to be `dev`-only (`if (process.env.NODE_ENV === 'development') {`)
* [ ] create a separate fork for each project
* [ ] when switching to a new project, consider adding optimizations to reduce time it takes to move between them (e.g. Webpack-related optimizations below)
* [ ] decide whether to use `npm` or `yarn`
* Test with `yarn@2`
* `yarn` is (currently) faster and more reliable than `npm` in most cases; probably prefer `yarn`, if it works
* [ ] make sure, dependencies are locked (should work with `yarn` and/or `npm`)
* check in `lock` file
* [ ] deal with binary dependencies
* generally avoid any binary building on the system, since it can go very wrong and is too far out of our control
* make sure that pre-built binaries are always available
* e.g. `sequelize` samples depend on `sqlite3`, but it appears that `sqlite3` pre-built binaries of old versions are deleted from their official download link when a new version is released
* -> we might have to consier removing `sequelize` from bug list as a result
* [ ] #615
* [ ] add a basic hint system? (some `todomvc` exercises already have hints)

This is a broad tracking issue with many completed and unchecked items rather than one defined task. Start by choosing a single unchecked item, then inspect the named entry points such as PracticeSession, ExerciseNode, BaseGroupNode.constructor, BaseTreeViewNode, or resetExercise; done is defined by that item's specific checklist and expected UI behavior.

Written by the indexing model from the issue text.