Character datatype isn't supported on filter operation

[karandashovrz]

Need to add supporting of caharcter datatype on filter operation with next options:
'=', 'in', 'notIn', '<>', 'notEmpty'

[artemglinov]

QA Notes

To test the fix, one needs to:

1. create an entity (e.g., NewEntity);
2. add an attribute of type Char (in the designer) which is actually of Character datatype (called, e.g.,charAttr);
3. create an entity instance (instances) with specific value (values) of charAttr;
4. send a GET or POST filter request as described in docs. It is possible to find an example of a suitable GET request parameter "filter" value in entitiesFilterCharAttribute.json file as well as an example of building a request in EntitiesControllerFT#loadEntitiesWithCharAttributeFilter test in restapi-demo project.

In order to determine "operator" value refer to RestFilterParser#findOperator method.