Implemented "MigrationManager.ShouldMigrateFile" utility method
Implemented "GenericTaskDialog" for use in notifying user of an obsolete file
Added "Controller.RequestTaskDialog" event handler to display task dialog
Implemented "MigrationManager.DisplayObsoleteFileMessage" helper method
Updated "TaskDialogParams.ClickedButtonId" data member upon button click
Updated DYN/DYF file loading code paths to display load fail dialog
Fixed a crash when Dynamo refuses to open an old DYF file
Merge pull request #1356 from Benglin/MAGN-2381

Disable file migration for 0.7.0