You can now pass in a 'download_url' attribute to a chart directive to
display a link for downloading that chart.
URLs for the overview page, and a bugfix that makes it work.
Bugfix incase the surveyor doesn't exist (happened with my dataset).
Moved the templates for the charts into actual templates.
Removing this as per #148.
Data download on all the reports! wooooo
Styled up the download links a little bit.
Merge branch 'feature/Data_download'