Add compatibility switch to allow empty argument values

Current Situation

• With release 2.5.2 a more strict behavior has been introduced not to allow empty argument values.
• The intention being that jobs should not have to make the distinction between arguments that have been specified and arguments that hold empty values.
• This behavior breaks the functionality of previous releases, particularly when it comes to migration from JS1 to JS7.

Desired Behavior

• A compatibility switch is introduded:
  • The Settings page holds a Boolean configuration item "allow_empty_arguments" in the "joc" section that by default makes the new behavior available (false).
  • Users can choose the value true for compatibility with the previous behavior.
• The switch will act on the API to allow empty values and it will act on the GUI.