Add tests for an experimenter_id of None
Marshaling screens
Some style tweaks
Fix and add test case for empty Screens
Add test for marshalling Screens and Plates with correct sorting
Add tests for an experimenter_id of None
Merge remote-tracking branch 'chris-gh/feature_5_0/webclient_tree_speedup' into feature_5_0/webclient_tree_speedup

Conflicts:
	components/tools/OmeroWeb/omeroweb/webclient/tree.py