fixing an missing check within vbo plugin against handlers and updating user_create_menu plugin to no longer display all roles as being added to a user type

finally integrated page_managers context with context_admin allowing for much greater flexibility with the existing plugin architecture and providing a path forward for some new potential plugins

added an additional handler that works with node types that have node references on them.  It allows for a node to be created with a reference to another node automatically.  No need for user input, the page setup does the work.