[#205] Add about text to publishing statistics front page

Provided by Bill
https://github.com/IATI/IATI-Dashboard/issues/205#issuecomment-58756288
[#192] Add explanation of timeliness methodology
[#192] Add link to the support forum
[#216] Update frequency calculation to count only increases
[#202] Add column for future transaction on frequency page
[#196] Use correct assessment order for javascript tablesorter
summary tables