Cooja updates

A bunch of Cooja updates. Highlights:

* Support for link-layer ACKs for Cooja nodes. This makes it possible to simulate RPL with correct link feedback.
* Improved stack monitoring and stack overflow triggering
* Improved radiologger: duplicate packets can now be collapsed into a single line and packets that don't reach anyone may be hidden from view
* Improved Timeline handling
* Save radio bitrate in .csc file