bit helper can not handle more than one single file

[c-hartmann]

title says it all. handling multiple files might be implementable by creating an
array of filenames from %F instead of %f and looping over these. there is probably
some effort to do so, but this will likely improve usability a lot.

[c-hartmann]

current situation. if multiple files are selected beforehand, the script is called multiple times.
in case of no errors, the user will not notice any problems. in case of errors instead, the user
will be confronted with multiple error message. this can get quickly, really annoying.