Renaming RTCIceTransports to RTCIceTransportPolicy

At TPAC 2014, we decided to rename "RTCIceTransports" to
"RTCIceTransportPolicy", but we never discussed it on the list or made a
tracking bug.  I have made a PR to do so:

https://github.com/w3c/webrtc-pc/pull/170


However, I had two questions for the list:

1.  Should we rename RTCConfiguration.iceTransports to
RTCConfiguration.iceTransportPolicy as well?  I think so, so I that's what
I did in the PR.

2.  Should we change the type of RTCConfiguration.iceTransportPolicy from
RTCIceTransportPolicy to DOMString?  During the discussion of
RTCBundlePolicy,  Jan-Ivar suggested that was a good idea because it made
it easier to add values to the enum in the future.  I don't care much
either way, but I'd like RTCTransportPolicy and RTCBundlePolicy to be
consistent.  We should either make RTCIceTransportPolicy a DOMString or
make RTCConfiguration.bundlePolicy an RTCBundlePolicy.  Which shall it be?