Serializer Section

Quick QA for the serializer section, which is pretty simple. As always, ignore the actual commits. Here are the steps:

- install jms/serializer

- create the serializer service

- add .gitignore    

- replace serializeProgrammer with serialize in ProgrammerController

- createApiResponse in BaseController

- fix null values in serialize() with SerializationContext

- whitelist properties
    - nickname
    - avatarNumber
    - tagLine
    - powerLevel
    -> test that userId does not exist

What about configuring the format here? We can still make `json` the default, but I think it is cheap enough and would make things a lot more powerful.