added selenium tests for population xml file uploading. Refs #201.
changed population objects to delete themselves if the xml file import failed for any reason. Refs #201
fixed test for population upload errors to desired behavior. updated view and javascript to display an error if the xml import failed. Fixes #201
fixed issue with large amounts of rows in the assign disease spread page causing the m2m widget to not generate properly. Refs #202
removed add option from bulk selectors on m2m widget. Refs #202
Merge remote-tracking branch 'origin/python-tests'