TextEditors: Move contentsChanged signal from editor to document

Change-Id: Ic935a8971705cb3238deda71aa2b5d19e4f62593
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
CppEditor: Fix semantic highlighting after "Save as"

Change-Id: I523735bae9e1a19678d4ab697c1edce2886bedeb
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
CppEditor: Do not reimplement BaseTextEditorWidget::setMimeType

It's not necessary, since we have signals for that. And it's wrong to
handle the additional preprocessor directives there anyway.
The update if the editor supports objective-c/c++ is now done in a
mimeTypeChanged signal handler, the update of the additional
preprocessor directives on filePathChanged.

Change-Id: If88c70f5321c2bc21a21673e96be2598dc9ecf04
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
BaseTextEditor: Remove some unnecessary indirections through widget

Change-Id: I4f71448d6788a4e553b1495b72263a004e65d8c0
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
BaseTextEditor: Remove unused method and member

Change-Id: I9b9081df454aae35c42744f4bbd385e8bd6c50d2
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
BaseTextEditor: Make internally used function static

Change-Id: I365e4c56b45dda205caa009e7733579d40bca9d0
Reviewed-by: Eike Ziller <eike.ziller@digia.com>