Adding pause/due date functionality

User's can now manually pause and unpause issues.
An issue's due date is also now calculated using these pauses, as well
as the set working periods and the estimated hours. The user's time
zones and working periods time zones (including daylight savings) are
also taken into account.
Small SLA status update

Issue's SLA status now shows if an issue is not currently being worked
on (out of office hours)
Small working periods bug fix

If no user time zone set, no time zone is shown next to "Shown in:".
Should show the Rails time zone.
Remove boolean time zone bodge

Making adjust_for_current_time_zone method accept the user time zone
instead of a boolean. Clearer.
Adding a pause list page

Adding a new page to display a list of all of the previous (and current)
pauses for the current issue. Button is located next to the
pause/unpause button.
Small display changes

Working Periods page now only shows one delete per actual working
period, regardless of time zone splitting.
SLA status now displays out of hours message in brackets next to regular
message.
Fixed pause bug

Pauses in the working period in which the issue is estimated to finish
were not being taken into account. This is now fixed.
Also remove flash message when pausing/unpausing.
SLA seconds now used instead of estimated hours

When calculating the due date, we now use the SLA priorities 'seconds'
field instead of the estimated hours field of the issue.
Fixed working periods hang

Issues were hanging when no working periods are set. This is now fixed.
Working period cleanup

Removed a few unnecessary methods.
"Shown in" line on working periods index page now takes daylight savings
into account.
Final merges because Alex fucked up.
Small working periods change

Added back button to new working periods page and also made page
redirect to itself on submit, instead of the index page. Should make it
quicker when setting up the working periods.
Merge branch 'master' of https://github.com/artsalliancemedia/redmine into sla
Out of working hours bug fix
Adding require lines back in

Whoops.
User user specified date formats

Now using user specified date/time formats for working periods and
pauses.
Fixed due date calculation bug

Due to pause related bug, could get due dates that occur before the
issue was started!