Extra features for large PR workflow

I just moved to Github from Gitlab and this extension is really great, thanks for building it!

I often have to review very large pull requests and there are a few features that help me quite a lot in my workflow, so I cloned the project and had a go at adding them. I was wondering if you're interested in having any of these:

* Option to filter by the full file path instead of just file name. I use this to review things like `api`, `src/main` and `src/test` separately rather than go file by file alphabetically
* Option to filter out file diffs as well as the tree view (so the diffs on the right hand side always match what's in the tree). This means I can filter to e.g. `api` and then scroll through all the `api` related changes
* A button to click "viewed" on all currently visible files. I use this to register that I've reviewed all the `api` stuff after scrolling through it, rather than clicking on each individual file

I put these features as optional settings in the options page, with them disabled by default.

Happy to raise a PR but wanted to check if any of these sound useful first. If not that's totally fine, I can see why you'd want to avoid the behaviour of the extension spilling out into other areas of the screen such as the file diffs! Also, I'm going to be using this a lot for work so I'll be more than happy to help maintain it

Below is a gif to show the features together. The benefits aren't very obvious on small pull requests, but I struggled to find really large PRs in open source projects!