Update Feedback Manager and Metadata Explorer to support generic view services

[dwolfson]

Need to update these classes to allow users to specify, for example, the view service to apply feedback to. Today, the query parameters in feedback manager are set with:

possible_query_params = query_string(
[
("isPublic", is_public),
("viewServiceUrlMarker", view_service_url_marker),
("accessServiceUrlMarker", access_service_url_marker),
]
)

So we need to remove the accessServiceUrlMarker and if the viewServiceURLMarker is provided, use it to replace the default URL marker (e.g. feedback-manager) with another module name. So viewServiceURL marker is also removed as a query parameter.