Telemetry functions

Replacing the old macros with functions. This is done by introducing a generic transport structure and a generic device structure.
It is only a small step on purpose, changing everything at once usually fails.

There is no functional changes, except that the transport and device for periodic function is passed as an argument, which will allow to create a telemetry task for logging in parallel of the normal telemetry (soon).

We now have:
- 4 transports (pprz, pprzlog, xbee, ivy)
- 5 devices (uart, usb_uart, sdio(chibios), udp, w5100)

This was tested on:
- lpc (pprz)
- stm32f4 (pprz, pprzlog, xbee)
- sim/nps (ivy)