Update to recent webrtc code
This updates the code to a recent webrtc
HEAD. This is a long-pending update, and in the process, more or less all the changes I made to the code itself are now unnecessary, and diffing is much easier. Hopefully we don't break other platforms in the process, but that needs some testing.
I've also updated the build system to version packages so that we can have parallel installs when breaking API changes happen, as discussed a long time ago on IRC.