Most lists in the app use (explicitly or implicitly) platform metrics for dimensions, text size, colour, and so on, possibly via styles.
A few don't, inadvertently using the user's setting for status text size
Fix these, and simplify code where possible.
- Use android attributes for padding and height, for consistent UX.
- Remove explicit usage of app:tabTextAppearance, rely on the style.
- Remove ListSelectionAdapter and item_picker_list.xml, and adjust TabPreferenceActivity to use an ArrayAdapter with simple_list_item_1.xml
- Simplify item_followed_hashtag.xml, consistent with item_list.xml.
Fixes https://github.com/tuskyapp/Tusky/issues/3131
* enable multiple hashtags in one hashtag tab
* add comment explaining the code in TabAdapter
* delete unused drawables
* add padding to EditText in dialog
* Theme refactoring
* disable the automatic tinting of surfaces with elevation in dark mode
* make the media warning visible again with the dark theme
* fix nav bar on api 27+
* use correct color for all media warnings
