Add basic support for data tags

This enables displaying data tags for data functions inside the
test tree. Clicking on the data tag opens the editor at the location
the respective QTest::newRow() call is done.

Change-Id: Ia91bf87437c2608a05bae88ed715711217685fdf
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@theqtcompany.com>