fix for latest report in overview

* report/latest/<node_name> uses limit parameter in _query
  to get just one report
* disable "Latest Report" button if there is no report
* HTTP Status 500 if there is no report on report/latest/<node_name>
error fix, format string and css button width fix
Merge pull request #36 from digitalmediacenter/fix-noreport

Fix for latest report if there is no report available