Save entries by default in the Form Dialog

[DanicaSTFC]

Closes #87

• Adds a method to UIFormWidget to populate the default widget states dictionary and one to make default widget states visible.
• Form dialog saves states by default when Ok is clicked and restores the previously saved states or the default states when Cancel is clicked.
• Add example file "dialog_example_3_save_default" to demonstrate the new features.
• Add example file "utilitiesForExample" for methods recurring in the examples.
• Add exampleState, set_state and test_dialog_buttons_default_behaviour to the unit tests.

[DanicaSTFC]

@lauramurgatroyd when you are happy with the PR changes I will resolve the merge conflicts locally.

[DanicaSTFC]

I merged the code with main (remove widget PR already included). The remove widget is not compatible with the default states because it deletes the widgets and the default cannot be restored. In particular, when we remove widgets and we press cancel, there is no way to restore the default widgets. The remove widget method needs to be changed for this PR to be merged with main.

Week 27 Nov - 1 Dec

After discussions with @paskino, we decided that we will save the removed widgets in a new dictionary. Thus, the remove widgets method will only hide the widgets rather than deleting them completely.

In order to finalise this PR, we need to use the insert widget method (PR #109) and widget number to reinstate the widgets in the correct location in the layout (issue #105 and issue #95).

Week 04 Dec - 08 Dec

We decided to merge this PR and leave the remove widget example returning errors when cancel is clicked. We will fix the problem in the other PRs.

[DanicaSTFC]

@lauramurgatroyd

The remove widget example is currently returning an error when cancel is clicked. This will be fixed once PR #109 is merged and issues #95 and #105 are solved. As discussed in today's group meeting, can we please merge this PR so the whole process becomes easier? Thanks.