Add Unit tests

[spacedmonkey]

Adding unit tests to menus and menu items.

I have also linted the code, upgraded coding standards, adding PHP 7.4 tests and fixed some bugs I have found while writing tests.

Three bugs I found.

• Delete item for menu items and the force flag.
• XFN is handles in arrays.
• Validation of invalid term ids.

[spacedmonkey]

All feedback from @TimothyBJacobs has been actioned.