Initial support for importing an existing site into Pantheon. Also refactored how site creation works.
Improve URL validation for site import.
Merge branch 'master' into import

Conflicts:
	terminus.drush.inc
	terminus.site.api.inc
Correcting syntax error in URL validation
Merge pull request #100 from pantheon-systems/import

Initial support for importing an existing site into Pantheon. Also refactored how site creation works.