Controller: Move client file declarations to `_client_files()` method (Basic)
Client Files: Pass directly from child to base `_client_files()` method
Admin: Refactor client file declarations
Client Files: Replace formatted/placeholder text with dynamic values in file declarations

* Context
* Dependencies
Merge branch 'rfr-client-files' into develop
Re-route all widgets through SLB (to handle widget activation)

* Update: Modify widget callbacks when SLB enabled (allows SLB to handle widget activation)
* Update: Check if widget is being processed in `SLB::process_links()`
* Update: Admin check added to `SLB::is_enabled()`
* Remove: Redundant `is_admin()` calls.

* Ref: Issue #125
Util: Update documentation
Add: Exclusion methods
Excluded previously-processed widget content from additional processing (Initial)

* Needs to be optimized/refactored
Merge branch 'activation-exclusion' into widget-reroute-callback
Set widget processing up for Group ID filter

* Add: Filter callback
Group widget output separately
Merge branch 'group-widget-output' into widget-reroute-callback

* Fix: #125
Merge branch 'widget-reroute-callback' into iss-125_widget-activation
Merge branch 'iss-125_widget-activation' into develop