Changing the controlled value was setting triggering immediately an
onChange event with undefined value. This was due to the fact that when
the controlled value was changed SelectMonoAux was searching only in
options displayed, where it should in reality be searching accross all
options.
fixes#162
Previously if the menu was opened and no there were no options to be
displayed it was just showing a tiny empty menu, this commit adds an
empty placeholder in order to make it clearer that the list is empty.
Adding this new variant makes necessary to reorganize the files to keep
a clear separations of concerns. As of now Select/index.tsx is just an
entrypoint to render either the mono or multi variant of the select.
