Bastion: System Bulk Actions: initial support for system group, content and remove actions

This commit contains changes to support the following system
bulk actions:
- Remove Systems
- System Group Add / Remove
- Content (Pkg/Pkg Group/Errata) Install / Update / Remove

This commit does not include tests.  Those will be added in separate commits.
Bastion: System Bulk Actions: support auto-attach available subscriptions

This commit contains changes to support the ability for a user
to perform the 'auto-attach available subscriptions to all systems'
to provide parity with the 'old tupane' functionality.

This commit does not include tests.  Those will be added in separate commits.
Bastion: System Bulk Actions: PR 2904 address comments
Bastion: System Bulk Actions: adding tests
Merge pull request #2904 from bbuckingham/bastion-system-bulk-actions

Bastion: System Bulk Actions: initial support..