System: complete UI refresh

[SKuipers]

This PR started as a few UI changes, inspired by HTMX and Alpine, and quickly snowballed into a complete UI refresh. It isn't a full rebuild, and aims to keep a lot of the structure of the UI the same (so things aren't jarringly different), however it makes quite a few changes to the UI, including the following (and some I'll likely forget to mention)

• New SVG icons that are crisp and scale well. Thanks to https://heroicons.com
• Updated all action buttons and tabs, with icons and better mobile support.
• Updated main menu and module menu, better mobile support.
• Updated the appearance of all form fields, which scale better on large screens, with better templates.
• Added quick-save keyboard shortcut when editing forms, which saves without reloading the page.
• Added a warning to all forms when navigating away if there is unsaved data.
• Removed outdated LiveValidation library with Alpine and browser-based validation.
• Removed jQuery Thickbox modal, replaced with Apline and HTMX-based modal
• Refactored the Planner and dashboard Lesson and Behaviour tables, which had not been done yet.
• Many, many other small tweaks and changes.

Motivation and Context
Moving towards a more modern looking UI with more responsive elements.

How Has This Been Tested?
Locally

Screenshots

[rossdotparker]

This is a very exciting addition to v28 : ) Thank you!

[fvlasie]

Wow! That is great!