[feature request] allow array of _other servers_ in settings

[j-lakeman]

In settings, when choosing Other server—requires LanguageTool server running there, it would be a great improvement IMHO if one could insert an array of LanguageTool instances. The order of the given instances could also determine in what order they're being used, e.g. localhost; languagetool.org. If the first instance times out after x ms, the second would be used, and so on.