change preset: piste:grooming=classic;skating to classic+skating

[GerdP]

The unusual form with + is used > 20000 times, the other ~10000 times.
I suggest to change the preset to classic+skating and add
K:piste:grooming=classic;skating
to ignoredtags.cfg.

[Klumbumbus]

At the beginning the wiki said classic;skating then it was ​changed 2010. I tried to ​fix it 2015 after a short ​discussion but it was reverted.
Looking at taghistory, classic+skating rose faster in the last years. Comparing with the latest numbers from taginfo classic;skating rose faster in the last about 9 months since the graph at taghistory ended. ID uses classic+skating.
Not sure how to proceed. I'm ok with both approaches (starting new tagging discussions with the goal to change the wiki and ID or change JOSM. The former sounds less promising to me...).

[GerdP]

I assume that consumers of this tag treat both variants as equal. Since the version with + is the favorite in the Wiki and in iD I think we should also go that way. In fact I like the '+' because it clearly shows that someone has selected both values in opposite to ';' which is also created when you combine two ways with different tags.

[GerdP]

In 14821/josm:

fix #17336: change preset: piste:grooming=classic;skating to classic+skating

There is one possibe glitch with this change: For typos like
piste:grooming=classic;skatin (missing last g) JOSM will suggest
piste:grooming=classic;skating instead of piste:grooming=classic+skating