* [CogManager] Correctly manage core and install paths
This keeps the core and install paths separate from those set in the
config.
It also displays the core path separately in `[p]paths`
Resolves#1982.
* [CogManager] Fix old reference to method removed in previous commit
Also did a bit of a general cleanup of cog_manager.py's code
* Make the core path a class attribute
* [CogManager] Paths should default to a list