Use REST API instead of xmlhttprequest

[vboctor]

The xmlhttprequest is being deprecated in MantisBT v2.3.0. Hence, snippets should publish its own REST APIs via the new framework and leverage that to power its functionality.

[dregad]

@vboctor I would appreciate if you could kindly review the commit I just pushed to https://github.com/dregad/snippets/tree/rest and let me know your feedback. Thanks in advance !

[vboctor]

@dregad done. Looks good. I have added few comments / questions to the commit.