Disable UploadField change detection in assets/admin/add

See https://github.com/silverstripe/silverstripe-framework/issues/2638
Refactor old page redirector into an extension
Merge pull request #801 from ss23/refactor-old-page-redirector

Refactor old page redirector into an extension
Merge pull request #889 from chillu/pulls/2638-uploadfield

Disable UploadField change detection in assets/admin/add
Updated translations