Make output of `read_config` and `read_config_file` fns a `<config>` class object

[annakrystalli]

In order to:

1. enable direct appending to config class objects read in from json files
2. as well as to retain class consistency between config objects created programmatically and those read in from json files

The output of read_config and read_config_file should be an object of class config.

To enable this, we should also move the as_config method from hubAdmin to hubUtils but re-export it back to hubAdmin for use there if needed.