Add default ports to PhutilURI

Summary: Add default ports to PhutilURI to allow the getPort() method to return the default port is no port number is explicitly provided.

Test Plan: Added test cases.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11338