add google chat handler

[nilesh93]

Add Google Hangouts Chat support for handlers

[shapirus]

a merge, anyone? :)

[shapirus]

btw will it be too difficult to add an ability to post everything in the same thread? on first call, google chat returns a newly created thread id in its response, which can then be used in subsequent requests.

[amit-uc]

Any plans for googlechat support?

[fannw]

+1 need this feature