Interface edits, additions, and fixes:
* Added a new module for exiting the client (client_exit).
* Added tab spacing to the UITabBar class.
* Added tab popup menus for things like channel tabs.
* Impelemented channel tab popup menus (still need to be finished).
* Fixed UITabBar tab draging (will now change after dragged half way over the
  next tab, not 2 pixels).
* Fixes to the client_options module.
* Edited some UI settings.
* Changed game_cooldown and game_spelllist menu button icons.
* Fixed some typos.
Merge branch 'master' of https://github.com/edubart/otclient