Replace SPARQL restrictions with restrictions on property paths

At the moment, dataset restrictions are expressed as SPARQL patterns.

Example:
{{?a rdf:type dbpedia:Film} UNION {?a rdf:type dbpedia:Musical}}
?a <http://dbpedia.org/property/language> ?lang .
FILTER(str(?lang) = "English")

This is not ideal for two reasons:

Difficult to support non-SPARQL datasources
Mixture of vocabularies

New Syntax from LDIF:

Restrictions are expressed as a combination of conditions. A condition consists of a path and a list of values. Multiple conditions can be combined using the and and or operators.

Example:

<Restriction>
  <And>
    <Condition path="/rdf:type">
      <Uri>dbpedia:Film</Uri>
      <Uri>dbpedia:Musical</Uri>
    </Condition>
    <Condition path="/dbpedia:language">
      <Literal>English</Literal>
    </Condition>
  </And>
</Condition>