Change campaign/campaignSpec URLs to include namespace and fit new schema

Created by: mrnugget

This is the result of our discussion of this item in our sync doc.

I think what we need to do is:

• CampaignResolver.URL needs to include the namespace: instead of /campaigns/$id it needs to be /user/$user/campaigns/$id etc.
• CampaignSpec.PreviewURL needs to be renamed to ApplyURL and also include the namespace.