Development -> Sand Box -> NAT traversal

Involved modules:

1. mediaproxy
2. nathelper
3. nat_traversal
4. mangler

nathelper -> nat_traversal

Nathelper module will be split into two parts - separating the communication with RTPProxy from the signaling and testing functions. The RTPProxy specific functions will be moved into a new module called rtpproxy. The signaling functions from nathelper module will be merged with the existing functions in nat_traversal module and the nathelper module will be permanently removed. Note that there will be no functional changes, but only structural ones, all current functions exported by nathelper module will still be available (some name changes might be possible though), just that they will be provided by the new module or nat_traversal module.

The motivation of this change is to provide a clear function separation (sometimes the rtpproxy functionalities are required, but not also the signaling ones) and also a consistent model (rtpproxy module will be similar to mediaproxy module).

Action plan: