Close mongo and casssandra terminal tabs once the shells are exited (#1183)

* initial commit for closing terminal

* added extra case

* lint changes and hostee explorer fixes

* fixed lint errors

* fixed compile error

* fixed review comments

src/Contracts/ExplorerContracts.ts

@@ -33,6 +33,7 @@ export enum MessageTypes {
   CreateWorkspace,
   CreateSparkPool,
   RefreshDatabaseAccount,
+  CloseTab,
 }
 
 export { Versions, ActionContracts, Diagnostics };