Add python widget for Bloch Sphere

[Scott Carda (ScottCarda-MS)]

Adds python support for the Bloch Sphere visualizer by making it a python widget, which is then added under the qsharp_widgets package, and additionally made available under the QDK python package.

Example python usage:

import qdk.widgets as w
bloch = w.BlochSphere('H T H') # string is initial gate sequence, can be empty
bloch

Additional fields added to the python bloch widget:

bloch.initial_gates # the initial gate sequence given when creating the widget
bloch.gates # the live gate sequence