Part 3 of the migration.

Part 2 here: https://github.com/actualbudget/actual/pull/1419

Moving the code to separate files. Functionally should be no
differences.

Seems to build fine, will test later.

This PR improves the consistency of the settings UI by moving everything
(except the budget name field on mobile) into `<Setting>` boxes.
Additionally, it adds a “Settings” option to the file dropdown menu (I
keep expecting it to be there, and I think it’s reasonable to expose it
in both locations so it’s easier to access)

*  (prettier) adding trailing commas

* More commas

* Make ButtonSetting more generic

* Add an “Experimental Features” section in the settings

* Fix text color

* Put experimental features behind another link

* Update Encryption.js

* Update FixSplits.js

* Remove unused variable

* That’s what I get for coding on my phone

Co-authored-by: Matiss Janis Aboltins <matiss@mja.lv>