Prepare Iteration components for manual mode deprecation

Update the Cadence create/edit forms

• Display a warning that manual cadences need to be converted to "automatic mode" with an explanation.
• Remove "automatic" fields from the iteration cadence create/update form.
• Deprecate the ability to manually add/remove iterations for automatic iteration cadences.

Update the Iteration edit forms

• Only allow the description field to be editable for iterations in automatic cadences.