Activities: Source code shuffle
 * Move all activities to single solution
 * Start teasing out most of the "meat" to domain specific solutions
 * Start renaming to make more use of sub-namespaces

TODO: Move all activity handlers from Activities solution to their domain solutions
TODO: Continue renaming to better use sub-namespaces
TODO: Rename activity "Utilities" to "Shared" (ex: EntityActivityUtilities -> Entity.Activities.Shared)