Move InputGenerator to QtGui

This moves the InputGenerator class from the quantuminput plugin
to the qtgui library so that it can be used by other plugins.

Change-Id: I249cc4077c31838e53e7fdd9f1e7ea4df9c91c76
Merge topic 'move-input-generator-to-qtgui' into master

3373250f Move InputGenerator to QtGui