added opdrachten in index.html

added opdrachten as an option voor documents, changed in man.css,
index.html and common_style.tex to include doc oprachten
review uitleg_HiSPARC

changed sentences and some typo’s
changed mistakes in checklist daq

deleted extra paragraph
changed checklist elektronica
Merge pull request #19 from HiSPARC/opdrachten

Added opdrachten for infopakket