EDataCal: Make GDBusMethodInvocation optional in operations.
EDataCal: Make GDBusMethodInvocation optional in operations.

Allows us to fake client requests, since ECalBackend's API is still too
intertwined with EDataCal to call directly.

Distrotech/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,Distrotech/evolution-data-server,Distrotech/evolution-data-server,Distrotech/evolution-data-server,tintou/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,Distrotech/evolution-data-server,tintou/evolution-data-server