SPARQLStore / QE / Split conditions, add SparqlConditionBuilder

- Individual condition are moved from SMWSparqlStoreQueryEngine
- Condition buidling has been moved into its own component to aid SRP
- SparqlConditionBuilder now takes in a Description and outputs a
sparql where condition
Merge pull request #383 from SemanticMediaWiki/sparql-qe-condition

SPARQLStore / QE / Split conditions, add SparqlConditionBuilder