Add { and } to cirtual keyboard and just save back settings that really were changed

I have to rethink the whole thing anyway since I just do this to prevent Koreader to write an entry to the persistent file when actually nothing has changed. I compare 1/8 to 0.125, and these are different strings but same values.
But with this new approach I consider settings exactly as changed when you click on "ok", so it should not matter anymore. I'll test it and probably remove this this whole gsub block with the next release.

Btw, in case you find multiple SEARCH_CALIBRE_PATH variables in your persistent just delete them. There was a minor bug that showed up when I invented SEARCH_CALIBRE_PATH2, should not happen anymore, but the old doublettes are still there.