Updated PX4ESC build for Pixhawk ESC 1.4

[bendyer]

This PR:

• Updates libuavcan to current master;
• Implements the new enumeration protocol;
• Adds the UAVCAN bootloader.

To build the bootloader:

cd px4esc/bootloader
make -j8

Build products go into px4esc/bootloader/firmware.

To build the application and make a UAVCAN firmware image suitable for loading via Pixhawk:

cd px4esc/firmware
make -j8 px4esc.image

Then copy px4esc/firmware/build/org.pixhawk.px4esc-bldc-v1-1.0.00000000.uavcan.bin to the appropriate location on the Pixhawk's SD card.

[pavel-kirienko]

Thanks Ben. As has been stated earlier, I want to restart this effort as an independent fork of PX4ESC (not FOC-capable) targeted for lowish-end systems. Now I'm planning to move these changes into master, abandoning the v1.5 modifications.

As a consequence of these changes, either this project or PX4ESC will have to be renamed. The current convention PX4ESC BLDC is really confusing.