[schema] Cache RQL expressions on schema loading Add a mapping rql string to rql statement Deserializing schema is ~36% faster with a lot (> 4000) expressions like those generated by cubicweb-container.

[schema] Avoid parsing RQL expressions twice on schema loading Kill full_rql (unnecessary) Use snippet_rql rather than rqlst when possible Don't access to rqlst cachedproperty from __init__ Deserializing schema is ~40% faster with a lot (> 4000) expressions like those generated by cubicweb-container.