Fix Beautify Anki in latest Anki version (2.1.49)

[fylux]

I have tried fix the add-on by simply spotting what part of the code was crashing and fixing it accordingly. I could trigger 3 different crashes and they were fixed in the following ways:

• self.bottom.web.setFocus() was producing inifinite recursion. Use self.mw.web.setFocus() instead.
• self._nextDueMsg() and self.next_learn_msg() have been deprecated after the TS + Rust rewrite (ankitects/anki@e568525)
• Apparently now webview.css and deckbrowser.css are in the css/ folder

Overall, these are very hacky fixes because in ankitects/anki@e568525 most of the logic that this add-on uses was rewritten so to fix the add-on further a complete rewrite would be required. It might be that there are more crashes which this fix does not cover since I was the only tester.

Tested locally on Windows 10, Anki 2.1.49.

PS: Thanks to @datphan310 for the reviewer.py fix. Before I was just naively commenting the code.

[ShoroukAziz]

Thanks a lot @fylux For your contribution. That seems to fix it for now.

[fylux]

Thank you very much for the review! Please don't forget to generate a new github release including this patch.

[ShoroukAziz]

Done already. Thanks Again!