When a user is allowed to make edits, show a normal edit button. When a
user cannot make edits, show the locked button.
This patch refactors edit button presentation logic into a new function,
updateEditPageButton(), which consistently updates the UI for both
enabled and disabled states. Additionally, in cases where the old code
only displayed the button via `$caEdit.removeClass( 'hidden' )`, the new
code now updates the state appropriately which is a functional change.
Finally, this patch sprinkles in some TODOs for future minor refactors
that were identified while creating this patch.
Bug: T190834
Change-Id: I083e91f0328cc057541ad42a27aae31b32b3d050
b106ed3219