Remove import of event_presentations.js from events.js because it has been set as a requireJS dependency

2 issues: 1) Prevent JS files to being cached by adding version parameter to the file 2) Move images slider code to main.js

Solves issue #41 (Preview presentation: Presentation titles occupy multiple lines even though there is free space)

Solves issue #37 (Pictures subfolder in past events) and #38 ( Presentations subfolder in past events)

FIrst part of "Set gray background color to the subscribe banner in Events and Home page but not in News page"

In upcoming events section, the width of the cards is not correct because the page structure is not identical in Plone than in the prototype