Creating a new database project, project items

* can create, open, and close sqlproj files
* can add sql objects to projects

extensions/sql-database-projects/src/models/tree/baseTreeItem.ts

@@ -52,3 +52,5 @@ export class MessageTreeItem extends BaseProjectTreeItem {
 		return new vscode.TreeItem(this.message, vscode.TreeItemCollapsibleState.None);
 	}
 }
+
+export const SpacerTreeItem = new MessageTreeItem('');