Fixed issue: repeatheadings didn't work with array_filter
Dev: repeated headings for array questions are generated as static HTML. In a case where an array question has an array filter, all the repeated headings are displayed even if no questions are visible.
Dev: added a javascript function updateHeadings and hooked it in
LEMrelXX in order to dynamically update array headings.
Merge pull request #150 from Grapsus/fix_dynamic_headings

Fixed issue: repeatheadings didn't work with array_filter