Improved display of issue's SLA status

SLA status in issue can now show that an issue is paused and in breach
(as well as out of working hours) at the same time.
Also allows a due date to remain when paused if issue already in breach.
Merge branch 'master' of https://github.com/artsalliancemedia/redmine
Small Issues Helper change

Changed the way I was monkey patching the Issues Helper. I now use
alias_method_chain instead of just alias_method.
Merge branch 'master' of https://github.com/artsalliancemedia/redmine
Changed due date calculation when in breach

When an issue is in breach, pausing will now further extend the due
date.
A small caveat is if there is a current pause, it is not taken into
account, as this would require constant recomputation of the due date,
which is something we are trying to avoid.
Removing puts statement
Removed due dates from journal updates

Changes to the due date no longer show up in the issue history, as it
can change often.
Annoyingly large monkey patch required though.
Merge pull request #67 from dannybutler/master

Improved display of issue's SLA status