This splits the backend into two parts: the local backend for desktop cellxgene and the AWS backend for hosted cellxgene. The local backend is in local_server while the hosted remains in server. The general idea is to copy everything from server to local_server, pull unneeded stuff out of local_server, and keep server as-is for this PR. Not touching server means all the infra and deployment code will continue working just as it did before so we can make those changes incrementally.
* split out config
* add tests for base and app config, refactor client config out of app config
* refactor default config retrieval
* create config test class and helper functions
* move default_config into server to fix import issue
Marcus Kinsella