Optionally notify admin on reservation creation

[orenyk]

Requested by ITG:

[O]ne feature that I would find very useful is to have an email notification sent to me (or admins) if someone reserves a piece of equipment. ... I think an opt-in setting for admins (probably an individual setting rather than a role setting) would be the best approach because not everyone may like to be notified.

We don't really have a mechanism for toggling e-mails for individual users (e.g. #914), but we can at least add an option to cc the admins on the "Reservation Created" user e-mail. I'll see if we can get it in v5.3.0.

[orenyk]

Ha, we don't currently send an e-mail on Reservation creation, so I'll just create an optional admin one.

[orenyk]

Just as a side note, I was planning on adding an optional parameter to UserMailer#reservation_status_update to add a cc to the admin e-mail so it could be optionally added to any e-mail. At that point it also made sense to switch the parameters over to a hash, most likely, e.g.

def reservation_status_update(params = { res: nil, force: '', admin: false })

[orenyk]

Ok, all done, and properly TDD-style too 😄. Just checking specs and then opening PR.