Informative error message if XSLT transform fails

[jan-niestadt]

If you use your own XSLT stylesheet, but it contains an error (e.g. a XSLT 2.0 function, which are not supported), Lexonomy will simply not show any articles, without showing an error message. It would be helpful to signal that something went wrong with the XSLT, indicating what the problem was and on which line it occurred; otherwise users are left to guess what they did wrong.

[jan-niestadt]

I see the error is printed on the console, so it's not a problem for local debugging. But users working on lexonomy.eu will still appreciate the feedback.

[gareins]

There is a callback in parse() command, which can be used to detect the error. However I think that this can be designed very similarly to how I am trying to redesign the database module (see #124) and then errors are handled automatically within "our" xslt module.