Using the .ui file instead of generated .py file for the samplechanger widget.
Restructured the creation of collections, so that a sample centring task is
added once per call to create_task. Instead of once per call to create_dc,
which resulted in multiple sample centring items.
Updated layout.
A sample centring task is now capable of centring several collections.
Merge branch 'master' of github.com:mxcube/mxcube

Conflicts:
	Bricks/widgets/create_discrete_widget.py