[web/calendar] fix regression in previous changeset "Enables css customization in CalendarView" was untested, and introduced a crash: TypeError: not all arguments converted during string formatting

usr/bin/cubicweb-ctl usr/bin/
usr/lib/python2*/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl