- Only generate resource pack mounts if the desired directory exists.
- Allow mounting files, as well as directories (fixes#90).
As always, also a wee bit of cleanup to some of the surrounding code.
- Abstract peripheral ID and type checking into separate class
- Update peripherals directly rather than marking as invalid then
fetching from the network.
- Update peripherals when adjacent tiles change
This does result in a slightly more ugly interface, but reduces the
amount of work needed to perform partial updates of peripherals, such as
those done by neighbouring tile updates.
