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
TouchMenu: added options to menu items with the following defaults:
keep_menu_open = false
hold_keep_menu_open = true
So, default for Tap callback is to close menu, and for Hold callback
to keep menu open.
In both cases, provide the TouchMenu instance as the 1st argument to
the callback functions (instead of a refresh_menu_func I added in #3941)
so the callback can do more things, like closing, refreshing,
changing menu items text and re-ordering...
ReaderZooming: show symbol for default (like it was done for
ReaderFont, ReaderHyphenation...)
TextEditor plugin: update the previously opened files list in real
time, so the menu can be kept open and used as the TextEditor main
interface.
SSH plugin: keep menu open and update the Start/Stop state in real time
ReadTimer plugin: tried to do what feels right (but I don't use it)
Also remove forgotten cp in the move/paste file code
