* Don't break `doc_pages` updates when it's completely disabled. (c.f., the commit's comment, doing it on every page turn seems a bit overkill, but I get that it's probably done that way because it was easier ;)).
* Detect the empty footerTextGenerator properly in `_updateFooterText` (it's `""`, not `nil`).
* Abort `_updateFooterText` early when the footer is invisible (and has been for a while/ever, i.e., when not requesting a repaint, like a mode switch would).
* Never send `SetBottomPageMargin` events twice.
* Minor tweaks to touchmenu & configdialog to avoid useless repaints (don't redraw the reader/fm unless we absolutely need to).
* Make sure we show the progress bar alone instead of nothing when disabling the last enabled mode in the menu.
Tap any part of screen to toggle bottom buttons visibility.
Swipe south to quickly close it (as long as image is scaled
to fit, and there's no need for panning).
And a couple bugfix this unearthed:
* Always set the default as the *current* value, no matter what (by chance, this was not an issue for margins).
* Don't crash on the hold gesture in the -/+ buttons for the horizontal margins (regression since #5303).
Thanks to <https://github.com/koreader/koreader/pull/5237> we can now extract the knowledge currently embedded in Transifex and put it directly in our source. This positively affects <https://github.com/koreader/koreader/issues/3754>.
Translation instructions and knowledge that comes out of localization-related questions should be preserved in the source, because Transifex is too ephemeral. For example, the links from <https://github.com/koreader/koreader/pull/2290> are no longer accessible. Even when they are, it's quite useful to have this information around while dealing with the code as well, and I also hope it'll be informative to contributors who seldom visit Transifex.
This commit also makes a few minor changes to obviate the need for comments where possible.
This commit standardizes the various todos around the code a bit in a manner recognized by LDoc.
Besides drawing more attention by being displayed in the developer docs, they're also extractable with LDoc on the command line:
```sh
ldoc --tags todo,fixme *.lua
```
However, whether that particular usage offers any advantage over other search tools is questionable at best.
* and some random beautification
* Make the cover thumbnail respect the cover's AR in the widget
* Add a "Mark as read/unread" button in the FM's longpress menu.
* Make sure the cover_info cache is wiped if necessary (sidecar purge/BookInfo cache clear).
The contained widget may not have integer position/dimen
(which should probably be fixed in those that don't ensure
that), and our maths could eventually make them even more
shifted by fractional parts.
In the end, when closing the widget, the refresh code may
miss painting/cleaning 1px and leave a border of the widget
on the screen.