Using more *::Constants::ICON_* where it makes sense and
wrapping the file names into QLatin1String where they were
missing.
The increased usage of the ICON constants needed a few more
cross plugin includes of *constants.h, here and there.
I think that it is OK, since the dependencies were alredy there
icon resource wise.
Adds a generic Outline pane to the sidebar. The CppEditor & QmlJSEditor
plugins will implement the IOutlineWidget/IOutlineWidgetFactory interface to
provide views specific to C++/Qml/JS documents.
Reviewed-by: con
