add results and locations to activities call

locations on list and detail, results only on detail
Remove elements from activity-list since activity-list inherits from activity
Merge pull request #82 from VincentVW/master

add results and locations to activities / activity-list api call
Change CharField/TextField empty handling

No null=True, default=None
Instead use:
null=False (= default) and default=“”
Merge pull request #84 from VincentVW/master

Change CharField/TextField empty handling