[Kst] improve ascii settings readability

[Peter Kümmel]

>    Branch: refs/heads/ascii-settings-cleanup

This makes the ASCII settings files more readable,
(it uses the XML tag names, not different ones).

But with this patch all existing ASCII file settings are
invalid, which means in the GUI it looks like the file
is opened for the first time.

All .kst files are still readable.

Is such a change OK, or is the code cleanup not worth
such a break?

Peter