Support Spark Max/Flex control modes other than Duty Cycle mode

[brettle]

For speed reasons, this is probably best implemented on the DeepBlueSim side so that it can use Webots methods as appropriate and avoid the round-trip communications latency that would be required if this was implemented in, say, lib199.

[CoolSpy3]

As a side note, this is already supported in lib199 as of DeepBlueRobotics/lib199#67. I agree that implementing this in DBS would probably be more accurate (and certainly more analogous to how it works irl), but I'm not sure how we'd send the necessary information without an update to the ws spec or some changes in how we handle simulated devices.