BUG FIX for Pull Request #2275: Fix the incorrect function calls

In PR #2275, all the individual Qt functions were changes from being imported individually to being references from their parent QtCore or QtGui module. Unfortunately, this pull request accidentally kept pyqtSignature and pyqtProperty (which were aliased Qt calls). This pull request changes the QtCore.pyqtSignature and QtCore.pyqtProperty calls from PR #2275 to the correct QtCore.Slot and QtCore.Property calls.