General GUI optimisations and atom selection inversion button

[ChiCheng45]

Description of work

• An invert selection button was added to the atom selection.
• Atom selection functions were optimized.
• Checkablecombo box has been optimized.
• Bond calculation in the 3D view has been optimized.
• apply_instrument has been updated so that the prediction output is only determined once.
• Changing certain settings that do not affect the output prediction will be faster as they will skip the output determination step.
• Fixed the time per frame so that the spin box is set to the same value as the value it is set to in the objects init. This means it doesn't suddenly change from 80 to 6 when it is changed.

According to my profiling tools, most of the time is taken up by the literal_eval calls in the ChemicalEntity objects. I think we should see a performance improvement with #616. We can make another PR to see what else can be optimized once #616 has been merged.

To test

• Load up a large trajectory and go to the 3D view, the trajectory animation with the bond calculation should be faster.
• Go to the actions tab and load up the atom selection helper, atom selections should be slightly more responsive. Check that the inversion button works as expected.
• Check that in a job like DISF, applying an instrument should be much faster as the prediction is only determined once.

[MBartkowiakSTFC]

It works. Big improvement for the GUI responsiveness when changing fields such as the output file name.