enable sort on text fields inside the data block

• enables sort on text fields (inside the data block)
• provide feedback to user if unsupported field is provided on SortQuery. Users will get error message:

{
    "code": 400,
    "reason": "Bad Request",
    "message": "Sort is not supported for one or more of the requested fields"
}

• resolves issue 44
• refactor & clean field type mapping implementation and move it to core package to avoid copying same code for all providers