Allow Nulls in ActionBase if JsonProperty allows it.
Add USBDownload, restructure USB Requests to have Options main peroperty.

- USBDownload added.
- USBIdentify, USBInitialize request models now have main Options
property like all other request models.
- USBDownload added to 'tests'.

closes #11
Merge remote-tracking branch 'origin/master'

Conflicts:
	ActiLifeAPITester/Tests/ApiTests.cs
Remove TestWaitForConsolePrompt
ApiTest to use GetValueFromJToken with extension in Library.
Show actual error from ActiLife in GUI, add icons for success/failure to GUI.