Hygiene: Rewrite things as Overlaynew

Make UploadTutorial an OverlayNew
ContentOverlay as child of OverlayNew
Kill LoadingOverlay
Remove use of dead code in nearby.less for .message - this
is not used anywhere from the look of it (looks like it
was previously used by PagePreviewOverlay which already
uses new overlay code so this rule doesn't apply)

This begins deprecation of the old Overlay class.

Change-Id: Icfdbdfde4ee831261d57013b4b790400d7426044
Merge "Hygiene: Rewrite things as Overlaynew"