Bugfix for multiple upcoming event lists, shown in one page

I've tried to display multiple reoccurring events within one single page and noticed, that 
the "show less/more" feature fore the occurrence list only works with the first one.

These changes will fix this:
- the eo-upcoming-dates is now a class, rather than an id. this will allow more than one within the website
- The Javascript implementation is changed to search for the eo-upcoming-dates class.
- It also avoids also creation of additional id's '#eo-upcoming-dates-more','#eo-upcoming-dates-pipe','#eo-upcoming-dates-more' which might also be created more the once.