Add support for organization webhooks with the sync button

[Mikaela]

https://github.com/blog/1933-introducing-organization-webhooks

I don't know how this should be done, but would it be possible to have organization appear as repository and set it to announce to channels and have all organization repositories announced?

[waddlesplash]

Tested and most events work (the preexisting ones -- push, branch create, etc.) New ones (e.g. repository create) return a 404 from Notifico.

[Mikaela]

I was thinking that they aren't supported, because sync button didn't notice them, but I will try. Thanks

[Mikaela]

I created webhook manually and GitHub says that it works, but notifico appears to have issues with freenode at the moment.

[TkTech]

Sync button's been poofed for awhile now, as the original feature required aggressive OAuth scopes that I don't want the liability of keeping.