Previously, options like `branch` and `name` (injected by the project
decorator for example) could be set using `METAFLOW_BRANCH`. They now
need to be set using `METAFLOW_FLOW_BRANCH`.

This change is made to prevent clashes between regular metaflow
configuration settings and decorator level options.

No other changes are made so `METAFLOW_RUN_MAX_WORKERS` still works
as expected and `METAFLOW_PYLINT` as well.

Several fixes:
  - fixed an issue with default values
  - better handling of parameter defaults as configs
  - handle config defaults as functions
  - ConfigValue is more "dict"-like
  - made <myflow>.configs and <myflow>.steps work properly
  - renamed resolve_configs to init

Specifically:
  - moved things out of the INFO file
  - added to_dict
  - renamed user_configs to config_parameters

Specifically:
  - made config values immutable
  - cleaned up state stored in FlowSpec
  - added a test exercising configs in various places

Will only print stuff when there is an error and will print it in a non-interleaved manner.