Improve working with files

I think, Autotool should always use UTF8 (independently of what local configurations define).

(We had runtime errors because of a "wrong" server setting.)

Therefore reading/writing files should use ByteStrings and manual de/encoding (see https://www.snoyman.com/blog/2016/12/beware-of-readfile/ for more details).

I guess most important would be a change here: interface/src/Util/Datei.hs.

Besides the configuration issue we would gain a huge performance boost (if we have similar speedups as in Michael Snoymans mini benchmark (see above): factor 20 on readFile).