Channel parts/quits with reasons should be able to have a different format than those without

[ShaneMcC]

Previously we had channelPart and channelPartReason formatters that allowed this, now we just have ChannelPartEvent

[ShaneMcC]

This also applies to channelKick/channelKickReason

[csmith]

I think the easiest way to do this is to allow very simple conditions for boolean fields (so the event will have a hasReason() method, and the formatter can define one option for each)