Silva SQL Source: remove LIMIT limitation

[Marc Petitmermet]

there is no possibility to override the default LIMIT=1000 in Silva SQL Source.

standard zsql-method objects have also a LIMIT of 1000. but this can be overridden in the advanced tab by setting the maximum rows to retrieve to 0. when this is set users can set their own LIMIT within the sql-query. maybe Silva SQL Source could just include such a field as well in the edit tab.