[webui] Introduces repositories controller

- Moved the following actions from project controller to repositories controller
  - #repositories -> #index
  - #add_repositories -> #new
  - #add_repository_from_default_list -> #distributions
  - #save_repository -> #create
  - #update_target -> #update
  - #remove_target -> #destroy
  - #repository_state -> #state
  - #create_dod_repository -> #create_dod_repository
  - #create_flag -> #create_flag
  - #toggle_flag -> #toggle_flag
  - #remove_flag -> #remove_flag
- Moved the following actions from package controller to repositories controller
  - #repositories -> #index
- Created new action in repositories controller
  - create_image_repository
- Removed has_flags mixin
- Introduced acts_as_list to RepositoryArchitecture and PathElement
- Moved tests from project_controller_spec to repositories_controller_spec