Translation flow for authors

### As a content editor, I want translations in Joplin to be consistent so that I'm not confused about how to enter translations.

### Save for Joplin 3.0
Long-term vision: If I make a change in English (i.e. add a step), that is pre-populated as an empty field in Spanish (and Arabic etc)

- [x] [Map translations](https://docs.google.com/spreadsheets/d/1KSZXcroWV-uPFNboYHH6inqJnMjgnzs4hrIqN-nLFxY/edit?usp=sharing)
- [x] Alternate language pages should be identical replicas of the english version by default, except for character count, which should be specific to the language. Authors should not have to re-create a page for another language, instead they should be created and updated using the english version as a master.

Additionally, tracking translations/english updates presents an even greater challenge:
- [ ] There may need to be some sort of notification mechanism for when english pages are updated, but not their non-english counterparts.
- [ ] There may need to be some overview which allows an author to see which pages have been translated into other languages
- [ ] There may need to be some mechanism by which authors manually notify the system that updates to translations are needed. I'm thinking that an author may make changes which update the "last updated" date, but which don't in fact necessitate a translation update.

See #2670 and #2744 for background.