Expose all async operations as tasks

[ohadschn]

I found a couple of places in the code that do async work yet don't expose a task (internally they do Task.Result):

box-windows-sdk-v2/Box.V2/Auth/Token/TokenExchange.cs

Line 88 in e13e25e

IBoxResponse<OAuthSession> boxResponse = service.ToResponseAsync<OAuthSession>(boxRequest).Result;

(exposed externally)

box-windows-sdk-v2/Box.V2/JWTAuth/BoxJWTAuth.cs

Line 186 in e13e25e

IBoxResponse<OAuthSession> boxResponse = service.ToResponseAsync<OAuthSession>(boxRequest).Result;

(exposed externally and used by both AdminClient() and UserClient())

[coolboy]

Thanks for your feedback, mark it into TODO list