Refactor filter application into own model

This also avoids storing an object in the overviews query rewriter
for the bbox filter (a plain data structure is used instead).

lib/cartodb/utils/overviews_query_rewriter.js

@@ -1,15 +1,17 @@
 var _ = require('underscore');
 var TableNameParser = require('./table_name_parser');
 
-// this is meant as a hack for development
-var queryBuilder = require('camshaft/lib/filter/query-builder');
+var BBoxFilter = require('../models/filter/bbox');
+var CamshaftFilter = require('../models/filter/camshaft');
+
 function apply_filters_to_query(query, filters, bbox_filter) {
-    // TODO: implement filter application here
     if ( filters && !_.isEmpty(filters)) {
-        query = queryBuilder.getSql(query, filters);
+        var camshaftFilter = new CamshaftFilter(filters)
+        query = camshaftFilter.sql(query);
     }
     if ( bbox_filter ) {
-        query = bbox_filter.sql(query);
+        var bboxFilter = new BBoxFilter(bbox_filter.options, bbox_filter.params);
+        query = bboxFilter.sql(query);
     }
     return query;
 }