kendo grid filter operators javascript
"eq" (equal to)
"neq" (not equal to)
"isnull" (is equal to null)
"isnotnull" (is not equal to null)
"lt" (less than)
"lte" (less than or equal to)
"gt" (greater than)
"gte" (greater than or equal to)
"startswith"
"doesnotstartwith"
"endswith"
"doesnotendwith"
"contains"
"doesnotcontain"
"isempty"
"isnotempty"