Update files for 1.7.3
Set MPC_NIGHTLY_RELEASE to 1.
Track selection: Don't override splitter choice if all tracks have the same priority.

Patch based on Kasper93's work.
Properties dialog: List tracks instead of pins when possible.

Splitters often don't output one pin per track so the streams list could be quite incomplete.
Update translations from Transifex:

 - Greek.