Issue 3705 data uri site logo

@SamPenrose, the parameter validation being part of dialog.js always bothered me, so I did an extract class to put all RP parameter validation into its own module - validate_rp_params.js. This reduces the amount of cruft in dialog.js and makes it a bit more obvious where to look when doing rp parameter validation.

There are two front end QUnit tests failing, I am unsure if these were failing before. 

This is to add on to the PR that you have issued against the main mozilla repo.