Deleted-assets-field

Removed support's *assets* field from *add* form.
Added tests checking if fields are shown in forms:
- (add|edit)(BO|DC) device,
- (add|edit) license,
- (add|edit) support.

Changed support urls to more suitable.

@ar4s  @quamilek 
```
'device_edit', kwargs={'mode': 'dc', 'asset_id': device.id},
```