Unique unicode for Day model

Address 1, 2, 3 from problematic dropdowns list.
Adjustments for schedule admin

Address 4 from problematic dropdowns list.
Adjustments to Presentation admin

Addresses 5, 6, 7, 8, 9 from problematic dropdowns list.
Sort categories

Addresses 10 from problematic dropdown list.
Fix error where object might be None
Merge remote-tracking branch 'origin/develop' into dropdowns
Merge remote-tracking branch 'origin/develop' into dropdowns
Admin adjustments to slots

To allow easier differentation between similar slots
Make slot unicode more unique
Merge pull request #289 from PyCon/dropdowns

Ordering in dropdowns