WIP: Groups support

[TheLastProject]

Group management:

• [x] Create groups
• [ ] Rename groups
• [x] Delete groups

Card management:

• [x] View groups (in edit view)
• [x] Edit groups

Filtering:

• [x] Group filtering

Unit testing:

• [ ] Create group
• [ ] Rename group
• [ ] Delete group
• [ ] View groups of card
• [ ] Edit groups of card
• [ ] Group filtering
• [ ] Hiding of group options if no groups exist