Return true if issue has the higher value among all the issue belonging to the same project (used from the
columView_template file to manage the display of the tools)
Return true if issue has the lower value among all the issue belonging to the same project (used from the
columView_template file to manage the display of the tools)
This class handles all the operations necessary to change the issues' value that are affected by an action made from
the issue navigator, and also the methods that are used within the columnView_template file to help display in the issue navigator.