Add timer lock

[ClaudiaMia]

Add a new lock type and an asset using it that allows to set a time and then lock the item with the set time.
Only after the timer runs out, the lock can be unlocked. That said, the person who locked the lock shall be able to unlock the lock even while the timer is still running.

While an advanced version could allow to define who is allowed to decrease and increase the timer, in the initial version this may not be needed, as the creator can at any time open the lock and lock it with a new time.