Add TitleBar widget
Add TitleBar widget

Existing widgets building their own title bar with help
of CloseButton should progressively be updated to use
this, for clarity, consistency, and less code duplication.

koreader/koreader,koreader/koreader,poire-z/koreader,Frenzie/koreader,NiLuJe/koreader,Frenzie/koreader,NiLuJe/koreader,poire-z/koreader