Auto log out after period of not being used

[brainchild0]

Currently, no option is available for automatically locking an open vault after a time period.

Thus, as long as the vault is open, data is exposed to any attacker who captures the device.

The open vault should revert to a closed state, or to one of PIN protection, after a period of not being used.

[binsky08]

Thanks for the requests. Sounds like really useful feature :)