Add customized data map to domain type

[longquanzheng]

Tested manually.
I will add CLI support after adding the thrift change to cadence-client repo and make a release.

longer@~/gocode/src/github.com/uber/cadence:(domain_data)$ yab -p 127.0.0.1:7933 --service cadence-frontend -t idl/github.com/uber/cadence/cadence.thrift  -m WorkflowService::RegisterDomain -r '{
>     "registerRequest": {
>         "name": "testdm1",
>         "description": "abc",
>         "ownerEmail": "lg@uber.com",
>         "workflowExecutionRetentionPeriodInDays": 123,
>         "emitMetric": true,
>         "clusters":[],
>         "data": {
>             "k1 ": "v1"
>         }
>     }
> }'
{
  "body": {},
  "ok": true,
  "trace": "0"
}

longer@~/gocode/src/github.com/uber/cadence:(domain_data)$ yab -p 127.0.0.1:7933 --service cadence-frontend -t idl/github.com/uber/cadence/cadence.thrift  -m WorkflowService::DescribeDomain -r '
>
longer@~/gocode/src/github.com/uber/cadence:(domain_data)$ yab -p 127.0.0.1:7933 --service cadence-frontend -t idl/github.com/uber/cadence/cadence.thrift  -m WorkflowService::DescribeDomain -r '{"describeRequest":{"name":"testdm1"}}'
{
  "body": {
    "result": {
      "configuration": {
        "emitMetric": true,
        "workflowExecutionRetentionPeriodInDays": 123
      },
      "domainInfo": {
        "data": {
          "k1 ": "v1"
        },
        "description": "abc",
        "name": "testdm1",
        "ownerEmail": "lg@uber.com",
        "status": "REGISTERED"
      },
      "failoverVersion": 0,
      "isGlobalDomain": false,
      "replicationConfiguration": {
        "activeClusterName": "active",
        "clusters": [
          {
            "clusterName": "active"
          }
        ]
      }
    }
  },
  "ok": true,
  "trace": "0"
}

longer@~/gocode/src/github.com/uber/cadence:(domain_data)$ yab -p 127.0.0.1:7933 --service cadence-frontend -t idl/github.com/uber/cadence/cadence.thrift  -m WorkflowService::UpdateDomain -r '
>
longer@~/gocode/src/github.com/uber/cadence:(domain_data)$ yab -p 127.0.0.1:7933 --service cadence-frontend -t idl/github.com/uber/cadence/cadence.thrift  -m WorkflowService::UpdateDomain -r '{"updateRequest":{"name":"testdm1","updatedInfo":{"data":{"k2":"v2"}}}}'
{
  "body": {
    "result": {
      "configuration": {
        "emitMetric": true,
        "workflowExecutionRetentionPeriodInDays": 123
      },
      "domainInfo": {
        "data": {
          "k1 ": "v1",
          "k2": "v2"
        },
        "description": "abc",
        "name": "testdm1",
        "ownerEmail": "lg@uber.com",
        "status": "REGISTERED"
      },
      "failoverVersion": 0,
      "isGlobalDomain": false,
      "replicationConfiguration": {
        "activeClusterName": "active",
        "clusters": [
          {
            "clusterName": "active"
          }
        ]
      }
    }
  },
  "ok": true,
  "trace": "0"
}

longer@~/gocode/src/github.com/uber/cadence:(domain_data)$ yab -p 127.0.0.1:7933 --service cadence-frontend -t idl/github.com/uber/cadence/cadence.thrift  -m WorkflowService::DescribeDomain -r '{"describeRequest":{"name":"testdm1"}}'
{
  "body": {
    "result": {
      "configuration": {
        "emitMetric": true,
        "workflowExecutionRetentionPeriodInDays": 123
      },
      "domainInfo": {
        "data": {
          "k1 ": "v1",
          "k2": "v2"
        },
        "description": "abc",
        "name": "testdm1",
        "ownerEmail": "lg@uber.com",
        "status": "REGISTERED"
      },
      "failoverVersion": 0,
      "isGlobalDomain": false,
      "replicationConfiguration": {
        "activeClusterName": "active",
        "clusters": [
          {
            "clusterName": "active"
          }
        ]
      }
    }
  },
  "ok": true,
  "trace": "0"
}

[samarabbas]

This looks good. Can you also add a test for inserting new values to the data map. Cover both situations where you add a new value and also update an existing value.
Also add a test for concurrent updates to data map.