Move File -> Load 180 Projection to Add / Replace Stack dialog

[MikeSullivan7]

Issue

Close #2367

Description

The option to load a 180 projection image has been removed from the File menu to the right click "Add / Replace Stack" menu in the file tree in the main Window.
Related View Tests have been removed to reflect the changes in the Main Window View.

Testing

make test

Acceptance Criteria

Load a dataset into MantidImaging without a 180 degree projection image.
Once loaded, right click the dataset tree in the Main Window and select "Add / Replace Stack".
Under "Image Type", select "Proj 180" and add an image, check that it loads into the dataset correctly.

[coveralls]

coverage: 74.202% (-0.02%) from 74.22%
when pulling 68f80e6 on 2367_move_load_180_proj_to_add_replace_stack
into 507d6e8 on main.

[samtygier-stfc]

Nice clean up.
I think MainWindowPresenter.add_180_deg_file_to_dataset can also be removed now. and maybe MainWindowModel.add_180_deg_to_dataset().

[samtygier-stfc]

Note: has updates to main_window_test screenshots