Improve article priority processing

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.0.5 GA
• Fix Version/s: --Sprint - SP, 6.1.0 CE RC1
• Component/s: Knowledge Base
• Labels: None
• Branch Version/s:
  6.0.x
• Backported to Branch:
  Committed

Abstracted out priority logic into a separate helper class to simplify code

Added offsets btwn priorities so that reordering of articles happens less frequently