Do not throw an exception for a query on proxies when proxies are disabled

If the proxies are disabled in the repository configuration with

<proxies enabled="false"/>

and the following query is run

SELECT * FROM Document WHERE ecm:isProxy = 1

it will raise a QueryParseException

Failed to execute query: SELECT * FROM Document WHERE  ecm:isProxy = 1, 
Proxies are disabled by configuration, a query with ecm:isProxy = 1 is disallowed.

It could be better to produce an error in the logs and force the boolean to false.
If the user does not get the expected result, we could hope he will look at the logs to understand why.

We could also use a configuration property to have a strict mode, set to false by default, which will keep the QueryParseException.