Co-authored-by: Toluwalase Agoro <toluwalase.agoro@stfc.ac.uk>

Adding missing unit tests for differencing table functionality

This commit does the following things:

(1) Sets the parent of the Muon Analysis GUI to be the main workbench window. This prevents the external plot sending the interface to the back.

(2) Moves the number_of_axes variable to the view.

(3) Adds in an external plotting button within the Plotting Widget View.

(4) Creates an external plotting model view class. This class delegates to either workbench, or mantidplot based plotting.

(5) Adds unit tests for the new feature

In doing this the unit tests for these functions has been moved into a workspace_naming test class.

The plotting kwargs has been moved into the presenter, to enable it to be changed based on view controls. Continuing to rewrite tests
Adding tests to cover the tiled plotting
Additional plot widget_model tests
Adding unit tests for plotting_widget

The pairing table wasn't updating correctly if an incompatible pair was entered into the table.

The tests have been updated based on the new columns present in both tables
Fixing failing tests
Correcting flake8 warning

Cleaning up the call to plot, such that it no longer takes a redraw option. This was chosen to simplify the logic, as the same plotting window is used throughout.

Adjusting the unit tests such that they test the new combined plotting widget.

for readability

Also fixes the tests under Qt 5. An uncaught exception from
lack of a mock class return value was not showing up as a
test failure in Qt 4.