Renamed MPfm.Core to Sessions.Core.
Renamed MPfm.Core.Tests, MPfm.Sound and MPfm.Sound.Tests.
Renamed MPfm.Library and MPfm.Player.
Renamed MPfm.GenericControls and MPfm.MVP.

- Tests solution builds correctly.
Renamed remaining projects/files.

- WPF and Android build successfully.
- Namespaces haven't been updated; this pass is only for renaming files
and projects.