Removed get/setBasicTitle() in IForm, removed private method
composeTitle() in AbstractForm, added unit-tests for property change
events. Removed unused member variable m_displayHintLocked.

Change-Id: I6d9858da8bab58ee5996309a2f40ce27ca5be328
Signed-off-by: André Wegmüller <awe@bsiag.com>
Reviewed-on: https://git.eclipse.org/r/38457
Tested-by: Hudson CI
Reviewed-by: Claudio Guglielmo <claudio.guglielmo@bsiag.com>