Add click on explore table cell to add filter to query (#12729)

* Add click on explore table cell to add filter to query

- move query state from query row to explore container to be able to set
  modified queries
- added TS interface for columns in table model
- plumbing from table cell click to datasource
- add modifyQuery to prometheus datasource
- implement addFilter as addLabelToQuery with tests

* Review feedback

- using airbnb style for Cell declaration
- fixed addLabelToQuery for complex label values

public/app/core/table_model.ts

@@ -1,5 +1,15 @@
+interface Column {
+  text: string;
+  title?: string;
+  type?: string;
+  sort?: boolean;
+  desc?: boolean;
+  filterable?: boolean;
+  unit?: string;
+}
+
 export default class TableModel {
-  columns: any[];
+  columns: Column[];
   rows: any[];
   type: string;
   columnMap: any;