Mouse, scrolling and a working UEFN install

Lists now take the mouse. Scroll the wheel to move through any menu and left click a row to pick it, so you are no longer stuck reaching for arrow keys your board might not have. Tab jumps straight to the end of a list and shift+tab back to the start.

UEFN installs were downloading nothing at all. That is fixed, along with the reason some builds reported themselves as available and then failed halfway through.

• Scroll the wheel to move through any list, and left click a row to pick it
• Tab jumps to the end of a list, shift+tab to the start, for keyboards with no Home or End
• New Mouse and scrolling setting, on by default, with scroll only and arrow keys only modes if you would rather keep the console's own text selection
• Fixed UEFN installs pulling no files at all
• Pruned chunks are now spotted on the mirrors that answer 403 as well as the ones that answer 404, so a part missing build is reported up front instead of failing partway
• Fixed Reset to defaults being quietly undone by the next setting you changed
• A locked exe now fails the release build instead of silently shipping the previous one