Preferences changes

A few more changes to preferences etc:

 * Make the difference between the main settings and deck options more clear
 * Add descriptions for each preference group
 * Move answer button size from fonts to reviewing
 * Edit some strings
 * Add an integrity check when changing the collection path
 * Issue 2012 -  remove rename option from deck options
 * Issue 2013 - allow deck options to open from longtap menu in deck picker