Frontend decides on initial load only whether to render a 404
After initial load, if the frontend router cannot match a URL,
then it will let the URL pass through and be handled by the server.
This obsoletes the need for marking URLs on the same host as
internal or external. They will always be handled appropriately,
e.g. customized links can point to pages within the app without
causing a full page reload.
Change-Id: I20adbf2ed18010e201a2075cb1c5a1ca9ac6dfdc
(cherry picked from commit 0d98136980)
00eda48100