Some misc cleanup to ProtectionForm

- Set variables near to where they are used in buildForm()
  and put variables that only need to be set once out of loops
- Move the definition of 'wgCascadeableLevels' javascript variable
  near the inclusion of mediawiki.legacy.protect module, so that
  this doesn't need to be set as a side effect of buildCleanupScript()

Change-Id: Ifb54723e7609f6fc5a8939e4fada5c2e664a22bd
Merge "Some misc cleanup to ProtectionForm"