Make it possible to contribute and use page providers at the core level, outside of a content view

Split content view classes, defined in nuxeo-platform-ui-web, into two separate packages:

1. nuxeo-services/nuxeo-platform-query-api, that will hold:

• PageProvider definition, moved out of nuxeo-core-api
• default page provider implementations, with a dependency to NXQL (and CoreSession)
• PageProviderService that makes it possible to retrieve PageProvider instances declared in extension points
• XMap descriptors for page providers, both useable by PageProviderService and ContentViewService

2. nuxeo-jsf/nuxeo-platform-contentview-jsf, that will hold:

• ContentView interfaces, as well as the content view service implementation
• ContentViewCache implementation
• ContentViewService now supports named page provider definitions, retrieving them using PageProviderService

Other Seam components handling content views (contentViewActions for instance) remain in other modules (webapp-core...).

Extension point names will not be changed => all the needed migration should be visible at compile time.