fixes #5183 - UI - Rename 'System' to 'Content Host'

This PR contains the changes needed in the UI to rename 'System' as 'Content Host'.

A few things to note:
1. This PR does not include changes to models, API or schema.  Based on discussions, the models/schema/API will continue to utilize 'system'.
2. This PR does not rename 'System Group'.  The goal is to rename those as 'Host Collections'; however, that will be done separately.
3. The PR includes several commits; however, I plan to squash them in to a single commit before merging.
4. Based on offline discussions, we renamed files/directories...etc for the files associated with the angular UI, to minimize potential future confusion that might arise from things being named one way in the UI, but differently within the actual code.