elasticsearch: refactor and cleanup

Move time series query logic to specific file.
Remove model parser and move to time series query file, adds parser test.

pkg/tsdb/elasticsearch/response_parser_test.go

@@ -2,9 +2,10 @@ package elasticsearch
 
 import (
 	"encoding/json"
+	"testing"
+
 	"github.com/grafana/grafana/pkg/tsdb"
 	. "github.com/smartystreets/goconvey/convey"
-	"testing"
 )
 
 func testElasticsearchResponse(body string, target Query) *tsdb.QueryResult {