chore(mount): add core type definitions

[EnergoStalin]

Part 1 of #91

Since code becomes fairly large after adding sshfs support and full typing i decided to go with some convention to remember api's which will be fully introduced later.

Rename self.partitions to self.entries cause UI becomes generalized.

refresh -> __refresh to make it more stand out as something internal cause later it shares first argument with fstype.

[EnergoStalin]

And actually maybe treating it as new extension would be eaisier for both of us. Cause 500/20 sounds like a crazy distribution do we really want 25 pr's for that? Feels like at least 3 weeks would be lost on this.