Allow configuration of working directory for custom commands

[markiewb]

See https://netbeans.org/bugzilla/show_bug.cgi?id=35582#c11

[dzsessona]

Added a comment there, here for convenience:

Regarding this #44 a workaround could be to run a command as:

(cd /whatever/folder; cmd)

If the problem is just the folder where the command will run. I will add it to the configuration as soon as i get a bit of time.