WIP: add different versions of some icons

[BigOlMate]

Modifies the UI icons to be a little clearer & higher contrast. As well as slightly higher resolution.

adds 28x28 variants of all icons
adds 14x14 variants of some icons

WIP because there's no code done and not exactly clear how to handle a number of issues:

• handling scaling/aliasing
• handling variable interaction boxes on buttons
• do we maybe want to handle arbitrary sized buttons and derive everything from the image itself?
• etc.

[m-m-0-m]

You could make this a draft PR.

[BigOlMate]

Done, never heard of it before, but it sounds like what WIP: prefix used to do, so I'll do it 👍 cheers

[IntegratedQuantum]

Better textures have been added in #406
The scaling/aliasing issue was solved by using 9×9 icons.