Party Select 2 - Party Bar

Added a party select bar to the UI, allowing the player to select party
characters by clicking on their portrait.

Also moved responsibility for whether or not to select characters
exclusively or add them to currently selected characters to the
PlayerPartyManager by the bool _selectorModifier attribute, allowing the
same function to be called in either event and the PlayerPartyManager
will decide what to do rather than requiring the caller to decide.