Spike Solution: JMS Serializer as a replacement for domain object decorators

This PR proposes the usage of JMS Serializer instead of our custom domain object decorators which aren't cutting it.

I have used a proxy for the JMS Serializer to make it easier to move to another serializer if we choose to do so.

TODO:
- [x] Install JMS serializer
- [x] Create solution for paginated JSON responses that are generated via the JMS serializer
- [x] Update Issue API actions so that they use JMS serializer
- [x] Update User API actions so that they use JMS serializer
- [x] Update Project API actions so that they use JMS serializer
- [x] Update Client API actions so that they use JMS serializer
- [x] Update backbone response parsing to handle new serialized objects