Re-revamping the BoxManager ctor

passing an IBoxAuthenticator into the constructor required that the
client include a reference to restsharp.dll, which is not ideal.  This
method simply uses the required values (v2: access token; v1: api key
and auth token) to create the IBoxAuthenticator internally.  No more
fiddling with optional tokens/keys.
Moved static methods closer to usage.