Out of working hours changes

When out of working hours, an icon is now displayed instead of text
(with a tooltip to give more info).
Unfortunately, to do this, I had to completely dismantle the
'issue_fields_rows' table structure and convert it to the raw html. This
was necessary, because otherwise the icon and tooltip options get added
to both the title and the text of the resulting row.

Also, this icon does not appear when in breach.
The icon itself is also temporary (an hourglass). Will get a proper one
when I hear back from Stig.
Out of hours fix

Accidentally made out-of-hours icon disappear when issue in breach in
last commit, rather than if closed as was requested. This is now fixed.
Removing out of working hours tooltip detail
Merge pull request #79 from dannybutler/out_of_hours_changes

Out of working hours changes