Tankobon

Changed

* The root manga index file (at `~/.local/share/tankobon/index.json`) is now compressed with GZip.
This should have significant space savings on disk, especially for large indexes (with a lot of manga).

Changed

* The bottom GUI in the toolbar now shows the correct colour icons (white for a dark system theme, and vice versa).
* Added locate button in the toolbar.

Added

* Dependency on [MangaDex.py](https://github.com/Proxymiity/MangaDex.py).
* Progess bar and about box in the GUI.
* Mangadex source (not complete yet).

Changed

* Versioning system is now based on date in the form of `YYYY.MM.patch`, where patch is the release number for that month.
* Renamed `tankobon.parsers` to `tankobon.sources`.

Fixed

* Checks for None when presenting Metadata objects in the GUI.
Previously, any None values would cause `TypeError`.

* Internal code reorganization.
* Removed the `catmanga` and `genshin` sources. (R.I.P Black Cat Scanlations)
* Removed dependency on fake_useragent in favour of an internal module `imposter`, which does the same thing.