Enabled value replacement for MediaResource.uri to serialize()

This allows ODIDMediaEngine resources with explicitly-specified URIs
 (e.g. DASH resources) to use substitution.

Tested resources with URIs of the form:

 uri=http://@HTTP_SERVER_ADDRESS@/DASH_AVC_TS_SD_ISO/Video/SD2_480_4x3.mpd

And verified the URI is correctly substituted in a CDS browse/search
 requests.