Renamed ExecuteSelectCommandAsync to SelectAsync.
Renamed ExecuteDeleteCommandAsync to DeleteAsync.
Addressed inheriting ModelCommand instead of implementing

IModelCommand in TransformableCommand.
Introduced new ExecuteAsync methods to pass several model instances.
Addressd new ExecuteAsync methods in ModelCommand.
Addressd new ExecuteAsync methods in CompositeCommand.
Addressed using ExecuteAsync(Keywords)

instead of ExecuteAsync(Keyword).
Merge branch 'improve-model-command-and-repository'