Bootstrap 5.3

[jcdhan1]

Closes #262

Upgrading to 5.3 and addressing breaking changes according to the migration guide.

[jcdhan1]

I also noticed icons inside buttons (mainly from the Page Form extension) look like this on the master branch using Bootstrap 4; there are barely noticeable minus and plus signs there.

So on this branch, I've replaced them with their fa-icon equivalents. Whilst fixing that, I've given the non-saving buttons a style similar to how they are on the Vector skin by making them extend .btn-outline-*. Vector is on the right.

Plain edit page

Form creation page

Example edit with form page (two text areas)