* Adds a new admin setting for experience levels.
This is used in the post management UI to determine the range of experience. These values fallback to the ones we currently see in DEV, Total Newbies and Senior Devs. There is also a removal of the word coding when talking about experience level, since the context for each forem instance should be implied when referencing experience.
* Cleans up experience defaults
* Fixes instance_of usage
