Add "multiple" option to possible field options, when kOptionsFormatter is used (helps in search queries)

I propose to add "multiple" field option to fields, that are using kOptionsFormatter class (in "formatter" option). Value in such fields is selected from limited value list, that is also set in field options (in "options" option). There is possible case, when user can select multiple values into same field (<select multiple></select>). When building search query we have no idea about value format, that is stored in field. For single value fields that value is stored as is, but for multiple value fields selected values are stored in "|ID1|ID2|ID3|" format.

Search query without "multiple" parameter:
`FieldName` IN (ID1, ID2)

Search query without "multiple" parameter:
`FieldName` LIKE '%|ID1|%' OR `FieldName` LIKE '%|ID2|%'