Fixed completion settings to also apply to the QML code completion

By moving the completion settings into the TextEditor plugin, so that
both the CppTools and the QmlJSEditor plugins can access the settings.

The user-interface to edit the settings is still in the CppTools plugin,
since we're in string freeze at the moment. It should be moved to the
TextEditor plugin later.

For now the QML completion only supports the case-sensitivity and
partial completion options, since there is no automatic insertion of
brackets.

Task-number: QTCREATORBUG-1327
Reviewed-by: Daniel Molkentin <daniel.molkentin@nokia.com>