Unify datapipe callback naming
Add missing prototypes
Allow using compositor service that is not lipstick

Separate ipc mechanisms needed during display on/off transitions
from ones needed only when full home screen is used. This allows
display to be fully powered off in act dead mode as long as the
act dead ui implements the compositor service.

As a transitional feature mce assumes that lipstick service handles
also compositor - unless separate compositor only service name gets
registered on the system bus.

[mce] Allow using compositor service that is not lipstick. Fixes JB#19566
Merge pull request #170 from spiiroin/allow_separate_compositor_service

Allow separate compositor service