POSIX::tmpnam -> File::Temp
bbbike-data/snapshot.cgi: exit gracefully on SIGTERM

A closed client connections seems to cause a SIGTERM to the cgi. Make
sure that temporary files are cleaned up in this case (this may make a
crontab entry unnecessary).

Also loop over the temporary .zip file contents instead of slurping
everything in.
BBBikeTest: zip_ok
test bbbike-data.cgi and bbbike-snapshot.cgi
run cgi-download.t test while deployment
data update (u.a. Friedrichsbruecke, Schiffahrtsufer, Platz der Stadt Hof...)