DDF-81 - use Apache POI 3.9.2

Tested each metrics output using a WebRunner (Selenium) script. 3.9.2 appears fine.
DDF-104: Encode dates in URLs, to avoid broken links

The problem possibly only occurs for non-negative UTC time offsets (since it looks like 2013-07-21T00:00:00+10:00)
DDF-104: Avoid deprecated method for URL encoding.

Merging in change from Brad Hards.