[Input] Refactored action implementation
[Input] Renamed joy() to joystick()
[Input] Action implementation: Negated filter

Specifying when events are chosen is more intuitive than when events are discarded
[Input] Simplified Action implementation further
[Input] Implemented custom actions
[Input, Time] Removed Listener typedefs, wrote full std::function types in parameter lists
[Input, Time] Added connect0() methods for nullary listeners