Allow multiple reservations in the same slot.
Do not allow users to have multiples reservations of the same asset at the same time.
Modified both AssetResources for getting the asset list by course
Added the possibility to edit assets of a course from teacheradmin interface
Enabled the possibility to edit pending and total allowed reservations
Remove a reservation if it's incompatible with its AssetAvailability.

When there's a change in an AssetAvailability instance, all reservations which
would not be allowed according to the new availability will be cancelled.
Handle assets slot time granularity

New settings option ASSET_SLOT_GRANULARITY will set the minimun possible time
which can be assigned to slot_duration.

The slot duration of each asset will be rounded to the nearest multiple of
ASSET_SLOT_GRANULARITY.
Send emails to users when a reservation is cancelled because an AssetAvailability has changed
Shows the concurrent reservations for each user reservation