Rename some internal things.

Remove mentions to "KF5", rename installer from lineedits to qt-wix
(since it will have more test apps than just that one), rename start menu
directory.
Remove the RemoveFolder for the start menu subdir.

Doing this "correctly" needs registry keys and other stuff I can't be
bothered with, and the only reason why it's needed is some obscure
roaming-profile scenario that I don't care about (ICE64, now ignored).
Turn off cabinet compression.

While testing, I'd rather get faster builds.
Remove more File/@Name attributes.

As before, they are redundant since they default to the filename in
the Source attribute.