Add Android MTP (Media Transfer Protocol) support

[tojamrok]

There are some CLI and windowed applications which allow file transfer via MTP (for example https://openmtp.ganeshrvel.com) but it would be good to have the network file handling in single place.

[mikekazakov]

If somebody wants to step in and implement such a VFS, cover with tests and maintain for the foreseeable future - PRs are welcome!
Personally I don't use any Android devices, so there's not much interest.