Redo columnDef.UnmarshalJSON

[illia-li]

issue #353.
Added 'complex_type' for all complex types of columns.
Redid columns 'UnmarshalJSON'.

Now complex type column description in JSON looks like it:

        {
          "name": "col5",
          "type": {
          "complex_type": "tuple",
            "coltypes": [
              "varchar",
              "smallint"
            ],
            "frozen": false
          }

Before can`t see complex type that is describe:

        {
          "name": "col5",
          "type": {
            "coltypes": [
              "varchar",
              "smallint"
            ],
            "frozen": false
          }

[dkropachev]

Since you are touching naming let's name value and key types properly in all complex types, i.e. ValueTypes, KeyTypes accordingly.

[dkropachev]

Please make a test to marshal/unmarshal cmd/gemini/schema.json