sort method for jquery.tablesorter

sort method for jquery.tablesorter

the sort method allows programmatic sorting as well as instantly sorting
the table when initialising the tablesorter; furthermore, the method can
be used to reset sorting (e.g. if rows have been added later via JS);
sortEnd event may be used to reapply alternating table row colours or other purposes

patch set 2: fixed mentioned issues and added another test
patch set 3: addressed all further issues, introduced more obvious way to
specify sorting
patch set 4: implemented sort method instead of using an event; reprashed whole commit message; introduced 'sortEnd' event
patch set 5: fixed white space error
patch set 6: Add release notes and rebase

Change-Id: Id14862100cd27ebd6980c48dcf497db229c4301f