Add variability factory for creating elements from UI.

Change-Id: I7de06ceecca6b7be878c371125c2a5e3a6140bee
Signed-off-by: Stefan Schulz <schulzs@mathematik.uni-marburg.de>
(cherry picked from commit ea2bc7b46b89c1ddbdd10ea92089c1155da19e8d)
25 files changed