Show option to download components for non-embed digital collections items.

• Includes an override of Blacklight's #document_index_view_type method that sets the view type to :list if the current action is :show. The view parameter can still be used to override this setting, but it will not set the view type by the session preference in the show view as it would normally. In the index view this will continue to behave as before with the default set to :gallery and a sticky preference that can be selected by the user from the main results view.
• Many, many updates to the portal configs so that the download button will always appear for components and the :is_part_of facet has a pretty label when applied.
• Had to modify SearchBuilder#exclude_components to accept an optional parameter that disables the filter when applied. This parameter gets added to links where the user clicks through to see the full list of components so that components are temporarily allowed to appear in the DC admin set.