Remove code in ViewEntityAction, duplicating Article::isCurrent()

also improved code that checks if viewing a diff

Change-Id: If2e6758f113dd0897d5aab67b84a4377cce6ac65
Split ViewEntityAction labelText code into several methods

Change-Id: I165720eed483299c1472eb160154ca3b96231eaf
Merge "Remove code in ViewEntityAction, duplicating Article::isCurrent()"
Merge "Split ViewEntityAction labelText code into several methods"