Install from URL should be deactivated while installing an extension via registry

[WebsiteDeveloper]

Currently when installing an registry extension, the install cancels without any notification. (Especially for big extensions like web fonts and edge-inspect)

[pthiess]

@dangoor Nominating for Sprint 30

[TomMalbran]

The install from URL dialog should be modal too, by moving the overlay behind it.

[njx]

Reassigning to @TomMalbran and marking fix in progress since he has a pull request up.

[RaymondLim]

FBNC to @WebsiteDeveloper

[WebsiteDeveloper]

@RaymondLim it is fixed now. Thanks to @TomMalbran