Bug 1952986: Add 'Emdedded URLs' to the developer menu

Related to bug #1856824 where we introduced a URL
conversion tool that was a hidden page. Now added
to the admin menu under 'Development',
called 'Embedded URLs', and placed below 'Style guide'
in alphabetical order.

Change-Id: I1692de5e29afdc1167a367369bd0ffefff5511c9