Implement required 2D navigation nodes in LCM

[tmplt]

The following nodes need to be implemented. A node that:

• [x] reads reported position from the DWM;
• [x] reads reported acceleration from the DWM; (not possible unless we switch exclusively to generic shell mode; switching TLV->generic takes a whole second) reimplement DWM node to query both position and acceleration via the generic shell;
• [ ] approximates the true position of the robot using the raw data from the DWM; (#12, #22)
• [ ] subscribes to all messages and forwards them to an external system for system visualization/debugging;
• [ ] regulates and actuates the motors;

(more to come)

[tmplt]

Additionally, investigate the following: https://github.com/lcm-proj/lcm/pull/175. Need we worry about out-of-order data? Perhaps we should log dropped UDP packets?