Should we rename XService classes to XEndpoint?

[matejdro]

Currently, all communication classes are named MusicService, SystemService etc., but they are not really services. They only facilitate communication between watch and phone.

I suggest that we rename those to the MusicEndpoint, SystemEndpoint etc. That way we can create MusicService in the app without naming conflicts.

@crc-32 what do you think?

[crc-32]

The original idea was to be roughly following the architecture of libpebble2 (https://github.com/pebble-dev/libpebble2/tree/master/libpebble2/services) but it might not be appropriate naming for how we want to use them