"prompt" and subsequent first "label" were not separated
in any way while second "label" and forth were; let's make
the resulting isolinux.cfg a tiny bit more pretty.

Its immediate purpose was influencing the GRUB boot menu
*but* the implemented mechanism is actually a part of the
long planned text branding and might be further merged
into branding when hierarchical features finally chime in.

So let's get the naming straight before it breeds.

- incompatible change (to fix the rather broken early style):
  use/syslinux/ui-% is now use/syslinux/ui/%;

- default timeout changed to 9 seconds (long enough and keeps
  the countdown in a single figure);

- added totaltimeout of 300 seconds;

- provided live kiosk images with almost-instant boot by default;

...and some other assorted tweaks here and there, sorry.

Back then I didn't come up with anything smarter than
"mkimage-profiles 2.0" (with my tongue in a cheek),
but as m-p has grown up to 0.4 it's time to fix this.

When done properly, all of the string should be brandable
(with some sane default value inheriting from image name),
but let's do it at least bit by bit.

Also included:
- reworked syslinux feature inclusion
- syslinux: s/textprompt/prompt/
- README++

- get rid of $dest
- work on features.in/syslinux
- README++