Deprecate API client constructors that take Context

[lbalmaceda]

The constructors that take a Context are going to be removed in the next version of this SDK. If you have were using them to pass the account, you can achieve the same result with the following code:

-AuthenticationAPIClient client = new AuthenticationAPIClient(this);
+AuthenticationAPIClient client = new AuthenticationAPIClient(new Auth0(this));

-UsersAPIClient client = new UsersAPIClient(this, "token");
+UsersAPIClient client = new UsersAPIClient(new Auth0(this), "token");

The README is already making use of the Auth0 constructors in the guidance.