Add Elseif branch to If Instruction

Feature

• The JS7 offers the If Instruction for workflows.
• Instead of using nested If Instructions users would like to find an Elseif branch that is more structured.

  if
      ifThen expression ...
      ifThen expression ...
      ifThen expression ...
      else ...
  

• The feature implements the functionality for Controller/Agents.
• For usability reasons a Case Instruction as suggested by JOC-1943 is offered in JOC Cockpit and will be mapped to an If Instruction using IfThens when deploying workflows.