Make `nengo-fpga` script

[xchoo]

Just as the nengo-gui has a installable nengo script, we should do the same for the nengo-fpga repo. Envisaged uses:

• nengo-fpga : Automatically starts up nengo (gui) with the nengo-fpga backend option. I.e., nengo -b nengo-fpga
• nengo-fpga --configure : Instantiates a text-gui to prompt user for information to configure the fpga_config file.
• nengo-fpga --get_dna <device name> : Queries <device name> for it's DNA value. I.e., calls out to the DNA_extractor.py script.

[xchoo]

Another use case:

• nengo-fpga --update <device name>: Updates the nengo- files on the board.