* 3647 Renamed ParentMetadata to DatabaseMetadata in FolderMetadata.cs. Removed Refresh function from IDataSource and DataSourceBase since it's not used outside of KustoDataSource. Added unit tests for ServerNode.cs. Removed unused constructor from TreeNode and unused AddChild function.
* 3647 Refactored KustoDataSource. Moved Set logic for DatabaseMetadata and columns into separate functions
* 3647 Reverted Rename of ParentMetadata in FolderMetadata. Reverted removal of Refresh function from DataSourceBase and IDatasource
* 3647 Renamed SmoModel directories to DataSourceModel in Kusto projects.
* 3647 Removed reference to Kusto.ServiceLayer in SqlTools.ServiceLayer
