Remove opaque text view only option
Move view transparency setting from document to windowController
Rename term "transparency" to "opacity" (fix #6)
Update documents
Make some methods private
Create new opacityPanelController
Replace previous opacity panel with new independent opacity panel
Enable ARC on CEOpacityPanelController
Localize OpacityPanel
Refine window opacity part in preferences window
Remove a deprecated defaults key
Clean code
Now lineNumView's background becomes also transparent
Use ARC on some classes (#49)
Merge branch 'refs/heads/feature/issue45_opacity' into develop

Conflicts:
	CotEditor.xcodeproj/project.pbxproj