[bug 1089650] Add a contribute.json file

Instead of asking all the usual questions like "Where is the code?",
"Where is the staging server?", "Do we have a mailing list?" you can
simply look all this up in the /contribute.json file.
[bug 1089650] Add test to verify that the JSON is valid

A test now checks if contribute.json is valid JSON.
Merge new code from master
Merge pull request #373 from bkowshik/master

[bug 1089650] Add a contribute.json file