bashrc: don't start xbian-config under screen/tmux

unlikely the user wants to see the menu again whenever a new screen/tmux
terminal is launched.
Remove add-ons, unnecessary thumbnails and default files.

See comments in 29815dfdbcc54b48021fd5202f3d73e3ca4b3eeb.
Merge pull request #1 from filippog/xbian-config-no-screen

bashrc: don't start xbian-config under screen/tmux
WIP: Remove unmodified files.

* .bash_logout, .profile get copied by useradd -md.
* RssFeeds.xml had default feeds, with a different URL pointing to FeedBurner
  vs xbmc.org.
* profiles.xml had default values.
* thumbnails get regenerated on first run.  Also, these were not expensive at all.
WIP: [debian] Update conffiles after 14865a170a205d4df4f6ae93e3cb1d34251f1e34.