Create an unprogrammed mode for fpga Processor

[BGull00]

Problem

Users should not need to have a physical serial connection to a physical FPGA to build a network and gather experimental data before runtime. For example, users should be allowed to view resource utilization for a given network without having the target FPGA physically on hand.

Proposed Solution

Add a should_program boolean parameter to the load_network method in fpga Processor. This should only program the built network onto the FPGA when true. should_program should default to true.

Hurdles

Most fpga Processor methods expect the network to be programmed onto the FPGA (e.g. run and apply_spike). To combat this, keep track of the fpga Processor programmed state and raise exceptions when users attempt to call these methods on an unprogrammed fpga Processor.

Expected API Impacts

Non-breaking boolean parameter should_program that defaults to true will be added to the load_network method in fpga Processor.