MythZoneMinder: finish the support for ZoneMinder >= 0.26.0

All combinations of capture palette and target colour space should now be
supported. This also moves all the processing to mythzmserver and always
passes RGB24 to the plugin.

Note: bumps the protocol version so both mythzmserver and the plugin need to
be updated.

(cherry picked from commit 68c07c49499ca5be40751bf59908bf03b242f281)