encapsulate iracingsdk

[dennis]

• Encapsulate IRacingSDK
• Initialize strings to an empty string

[dennis]

Oh. I rebased - I forgot you had reviewed it.

I changed a few things:

• Added an IState interface and ISession interfaces, which The State and Session implements. These pretty much maps from IRacingSDK to Slipstream world.
• Added TestState and TestSession that also implements the interfaces above. These also have setters, so you can control them as you wish, without getting into IRacingSDK land.
• Rewrote tests to use this