ENYO-2694: map plugins static files as `/res/plugins/<service-id>/*` … 

Instead of each plugin to have to run its own Node.js server (even when
there is no logic in addition to templates/libs/sources), this change
causes ares to centralize static file mapping.

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>