htmlreport: make link to index page ("Defect list") fixed on the screen so we can always access it regardless of how low we scrolled.
htmlreport: remove redundant <style> tags, make html output readable.
htmlreport: splitup HTML_HEAD where we want to insert the list of errors.
htmlreport: show index of errors of current page under Defect List link.
htmlreport: make content div overflow the menu properly when scrolling horizontally.
Merge pull request #330 from matthiaskrgr/htmlreport_2

Htmlreport: minor cleanup, write index of errors (with links) under "Defect list" in menu for each page