Better visualize stats/summaries on the call graph

Three goals:
1. Make stats/summaries more visual by adding **icons**, **tooltips** and better **formatting**
* → one tooltip for text+icon; should suffice to use `title` attribute.
* → use a new `function formatNumber` for each number
* → `function formatNumber(x) { return x.toLocaleString('en-us'); }`
1. Add more/better stats/summaries to call graph nodes.

## TODO

* [x] add icon for `nTreeContexts` (amount of all descendant nodes in subgraph)
* title = 'Amount of child contexts in subgraph'
* [x] add icon for `nTreeStaticContexts` (amount of all descendant static contexts in subgraph)
* title = 'Amount of static contexts involved in subgraph'
* [x] add icon for `nTreeFileCalled` (amount of files touched in subgraph)
* title = 'Amount of files involved in subgraph'
* [x] add new stat: `nTraces` (also w/ icon)
* title = 'Amount of traces in subgraph. This is a rough measure.'
* [x] add new stat: `nPackages` (use `packageName`)
* [x] rename `moduleName` to `packageName`
* [x] also enable these stats for ACG nodes (refactor to use the same code, don't copy+paste)
* [x] add a button to `Toolbar` to allow toggling stats

## More stats (w/ icons):

* [ ] amount of static branches (IfStatement, TertiaryExpression, Loop) that were executed
* [ ] amount of asynchronous schedulers
* [ ] amount of static loop statements that were executed
* [ ] amount of static executed lines of code (maybe? → requires some algorithm to accurately count loc)
* [ ] allow toggling *individual* stats: #478
* [ ] label CGRs (call graph roots), indicating what kind of CGR they are (e.g. what kind of asynchronous event scheduled them)