fixes #5191/#5193 - rename System Groups to Host Collections

This PR contains several commits to support renaming "System Groups" to "Host Collections" throughout the application.  The commits will be squashed in to a single commit before the PR is merged to master; however, thought this might be useful to reviewers.

The areas impacted include:
- file/directory renames
- schema/migrations
- routes
- model/controllers/helpers/views
- ui
- tests/specs

The commits do not change the interactions with the 'system', since the decision was previously made to only change system within the UI/CLI without impacting the API/models/schema.  As a result, host_collection.systems is still valid.  In the future, when we address the 'system' internally, we can also address how it relates to the host collection.