Enables completion for function declarations inside qml files.

Done-with: ckamm

Add the snippets to the completion box when the character at the left of the text cursor is a delimiter.

Done-with: Christian Kamm

Store the error message in the QTextCharFormat of the extra selection.

Activate the global completion when the the character at the left of the text cursor is a delimiter.

Move code to Foldernavigationwidget as static utilities and use
them from there and from the Project explorer. Fix error message box.
Task-number: QTCREATORBUG-62

The Navigator "called back" to the model in case e.g. the id
of an item changed. This was catched by the WriteLogger, which
lead to an assert.

Fix this by tracking whether we are changing the navigator items
due to a model change, and not reacting to itemChanged signal
in this case.

hoping for better performance. On this occasion, add context menu
containing "Open" and "Choose folder" enabling drive changes on
Windows. Purge remains of QDirModel elsewhere.
Task-number: QTCREATORBUG-62

Task-number: BAUHAUS-120

Yet another quick and dirty hack while waiting for the real binding pass.

potentially reduces the number of file::exists() calls