Allow for "item-less" equipment models

[orenyk]

From UP:

We have items like music stands which are all identical and we don't need to track them individually. We'd love to simplify the check out process for itms like these, to remove the necessity to select a particular music stand for each one a user is checking out.

This is something we could potentially implement, maybe having equipment models that just keep track of equipment item counts in the database without requiring actual equipment items. Ultimately we could move all availability tracking to counter caches (see #1501 for lots of work on this), but I'm not sure this make sense. Either way, wish list for now.

[esoterik]

It seems like the motivation from the client for this feature is to make check out easier. We could simply add an option on the equipment model that automatically selects the item at check out from the ones available

[orenyk]

Sure, that's another way to go about it. It would be nice if we could also simplify the inventory management for those models, e.g. you can just increment / decrement the number of items you have.