Added insertTemporaryBeforeCurrent method to add a pre-game phase
Added Mulligan functionality to game model
Corrected according to recent changes for events and actions
when currentEntity is null, all actions are no longer prevented
`UseAbilityMessage` now supports an array of targets
Cleanup of Json Deserialization
Merge branch 'client-server' of github.com:Cardshifter/Cardshifter into issue10
Made sure that non-cards can't be targeted for Mulligan
Dirty fix for stand-alone game client to simply skip Mulligan step
Added support for Mulligan and other multi-target actions in game client