Just save settings that really were changed

And not also settings that are different from the ones loaded.
This prevents Koreader from overwriting your complete persistent.defaults.settings when you started Koreader with a malformated persistent.defaults.settings file and choose "save settings". In such a malformated case you just can edit the damaged setting and save it back (although you can't see which one is damaged since the defaults settings are taken)
To edit arrays we need { and }

I removed pi and e and two other characters that were there twice and replaced them by {, }, [, ]
Merge pull request #819 from WS64/master

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