logilab-database #132587 add overideable dictionary on advanced helper for python -> db type conversion [validation pending]

this would allow to factor out some code from cubicweb, as well as properly overriding type conversion when needed (eg adding new base types)

done in1.10.0
load left0.000
closed by#3c58962f468c add TYPE_CONVERTERS dict on advanced helpers defining conversions callback from Python SQL types (closes #132587)
patch[sqlgen] Allow to unprotect some parameters during the creation of an SQL INSERT query [applied]