[OSX] Allow joining chat from gc2:// protocol URI

[mixflame]

Register a handler and some kind of plugin. Just open server list and fill out the settings except handle

[kfatehi]

Great feature.

Not useful for twitter marketing since URLs seem to be blocked from hashtag feeds, so I wouldn't necessarily bother.

[kfatehi]

but yes I support this. especially if you plan to add the iOS label too

http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/AdvancedAppTricks/AdvancedAppTricks.html#//apple_ref/doc/uid/TP40007072-CH7-SW18