Make Custom Fields Searchable

Currently we can't Search on Front End in Custom Fields that have list of values since selected Values stored as IDs and actual values loaded on request when displayed.

Currently "kSearchHelper::buildWhereClause" method is called at the end of OnSimpleSearch event. This method adds all keywords with LIKE type filter. I propose to create copy of this method, but instead of LIKE filter that new method should be calling "kSearchHelper::getSearchClause" method instead. Last of mentioned methods creates search sql for field based on it's formatter and data type.