Support custom json object in JS client
- Added connection.prototype.json which is initialized as window.JSON
- Changed default ajax content type to text
- Added connection._parseRespons helper to parse ajax responses from text to JSON (when it's not JSONP)
- Update all JS client code to use connection._parseResponse
- Added unit & functional tests
- Updated affected tests
- #1564
Code review feedback for JS client custom JSON:
- Change use of "self" to "that" in JS client
- Added unit test to ensure custom JSON object is unique (not shared)
- Corrected places where it was not calling into the helper method
Run JS client JSON unit test for connection & hubConnection
Fix JsonFacts.js test
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