Roster: Code cleanup.

Removed useless code.
Roster: Updated copyright.
Roster: More cleanups.
GmCellRenderer: Updated widget so that it works with latest GTK+.

Ensure we use the theme size for the created expander.
RosterViewGtk: Improved roster layout.

- Added the possibility to change the foreground/background colors.
- Added a different column to display an avatar.
- Fixed paddings.
GmCellRendererExpander: Renamed file according our convention.
GmCellRendererBitext: Merged from master.
GmEntry: Added new GmEntry widget and use it in Forms.

That new GmEntry widget is a enhanced GtkEntry with more features:
 - It can be associated with a validation regex. The GmEntry content
   is considered valid if the regex matches, or if it is empty and the
   allow-empty property is set to TRUE.
 - A GmEntry emits a validity-changed signal when their validity
   changes. It allows user programs to make the OK button unsensitive in
   dialogs as long as at least one GmEntry is considered as invalid.
 - A GmEntry displays the edit-clear symbol for quick content deletion
   when they are not empty.
Dialpad: Improved visual layout.
GActorMenu: Seperate different Actors into different sections.
CallHistoryView: Improved visual layout.

- Use more modern icons for missed/placed/received calls.
- Add an "error" error when we have a missed call or an unsuccessful
  placed call.
Accounts: Added registration transition status.

This is required by most account types.
It will also allow a visual representation of the registration status
(if any) in the roster.
RosterViewGtk: Display account registration status.

- Display a GtkSpinner next to the Account name when the Account is
  in processing mode.
- Display a registration status next to the Account name. It allows
  indicating if the Account is offline, online or in failure mode.