IEEE 802.11p device

This is the first of two code reviews for Junling Bu's GSOC project for ns-3 on the WAVE MAC models.

This patch provides an 802.11p device in a new module src/wave.  This device behaves, at present, very similarly to an existing ns-3 WiFi Adhoc mode device, but lays the groundwork for later WAVE modifications such as alternating channels (the second GSOC patch).  This patch allows the user to configure an 802.11p device that does not try to associate with other stations, and that operates in the 5.9 GHz band, and that includes support for vendor-specific action (management) frames, and helper classes that parellel those found in src/wifi.