Add board or architecture selection

[soundanalogous]

User should be able to select either board or architecture. This will generate a Firmata sketch that properly supports the selected board. For many boards this would not make any specific changes, however for ATmega32u4 boards the serial port would be handled properly. It would be helpful in knowing if the selected board has enough memory to support all of the selected features and if not, warn the user. Also if conflicting features are selected (use the same HW timer for example) then the user could be warned of this as well.

An example of a board would be Leonardo, Uno, etc. This will be a long list.

An example of architecture would be ATmega32u4, ATmega328p, etc. This would be a shorter list, but fewer users may be aware of what microcontroller their board actually uses.

Perhaps the user facing list is a list of all supported boards, but internally compare architectures.