The «here» is dead, long live the «context»!

Looks like already in the time around Zope 2.7 it was already an old
alias for «context»:

http://comments.gmane.org/gmane.comp.web.zope.plone.devel/19657
Don't show the waiting list section if no slot has one

When none of the slots has a waiting list, it can be confusing to the
user to see the reference to a feature that is not available when
choosing the timeslot.
Minor enhancements of messages for the user
Merge branch 'mcmaster-carms-v3'