Spec 3.1.1: Add "include" and "omit" URIs for LDPC

[scossu]

For containers only, add support for:

• http://www.w3.org/ns/ldp#PreferContainment
• http://www.w3.org/ns/ldp#PreferMembership
• http://www.w3.org/ns/ldp#PreferMinimalContainer

According to https://fedora.info/2018/11/22/spec/#ldpc