Improve update method for AbstractPlatform

[andrea-pasquale]

The implementation of the update could be improved given that currently we check manually for every single entry in the dictionary which passed to the method.
It would be nice to move to something simpler as noted by @stavros11 here.
I think that using a DesignPlatform with the refactor of the AbstractPlatform in #387. This should be quite easy to do.
However, as long as we have also the Multiqubit platform we need to provide a way to make this update work also for this platform. Although it will be preferable to move also qblox to the DesignPlatform asap.

Morever, we should increase the coverage of the update method.