Added lables for youngest and oldest instances for a role in the instances view.

The labels are added to make it easy to find the oldest or youngest
instance for a role at a glance.  This is especially useful when
deciding which instances to terminate or which ones to check for
latest updates.
Fixed bug where Oldest and Youngest label would both appear if only
one instance was available in the instances view.
Merge pull request #71 from krieb-r7/master

Added lables for youngest and oldest instances in instances view