Command UI fixes

* Fix memory leak in Command UI
* Stop refreshing command list on every UI refresh
  (This was causing the tab bar to flash on Gajim contacts, for example)
* Never hide the Command UI during an active session
* Allow text selection in Command UI tables
* Show desc text on Command UI embedded webview, when present

Also:

* Always show name of sender in global message search results
* Monochrome version of icon for use with Android 13 themed icons
* Several crash fixes