Group translation keys by sub-key instead of prefix
Group translation keys by sub-key instead of prefix

- Adds new sub-keys to replace key prefixes, and adjusts key names accordingly.
- Moves several button strings from `admin.permissions_` to `admin.permissions_controls`
- Merges `forum.settings_notify_` strings into `forum.settings`
- Rolls `forum.user_avatar_` strings into `forum.user`
- Moves the `user_deleted_text` to the `lib` namespace.
- Adds four other leftover strings to the `lib` namespace.
- Includes minor changes to formatting and comments.

pladask/flarum-ext-norwegian-bokmal,flarum/flarum-ext-english,flarum/english,FlarumChina/flarum-ext-simplified-chinese-pro,ogioncz/flarum-ext-czech,FlarumChina/flarum-ext-simplified-chinese-pro,pladask/flarum-ext-norwegian-nynorsk,ogioncz/flarum-ext-czech,pladask/flarum-ext-norwegian-bokmal,balkanje/flarum-ext-bosnian1,gtugablue/flarum-ext-portuguese,raweba/flarum-ext-danish,pladask/flarum-ext-norwegian-nynorsk