FileMaker Cloud Authentication

[heebinho]

Finally I found some time to work on the FileMakerCloud Authentication. Some thoughts regarding this pull request:

• As you have suggested, I've placed the aws packages in a separate project with the name FMData.Rest.Auth.FileMakerCloud
• I thought it's important to have the "full marketing name" at the end (FileMakerCloud), so that newcomers will easily understand the principle and that "following" implementations (Google, Microsoft Azure AD) will/can fall in place.
• The AWSSDK.CognitoIdentityProvider is not compatible with netstandard1.3 - this is why I have removed it from the target frameworks in the new project
• The Amazon.Extensions.CognitoAuthentication is not compatible with net45 - this is why I have removed it from the target frameworks in the new project
• I have added a new ctor in FileMakerRestClient, which is used like:
  new FileMakerRestClient(new HttpClient(), new FileMakerCloudAuthTokenProvider(conn));

What do you think? I'm happy to discuss and improve.
Currently I do have access to a FileMakerCloud account and can test.

regards,

Renato

[fuzzzerd]

Thank you for the pull request! I will review soon.

[fuzzzerd]

LGTM!