Add a Uri class.

Add a Uri class.

Add a Uri class matching our mw.Uri JS class for handling uris.
This class should be helpful in a bunch of places where we end up doing manual
concatenation of things like the path + '?' + query of a url parsed with wfParseUrl.

[tylerromeo@gmail.com: Removed cat() function, fixed wfWarn() usage for aliases
 and added visibility to all functions. Also added test for aliases.]
Signed-off-by: Tyler Romeo <tylerromeo@gmail.com>
Change-Id: Iefdedb7c80cf1d4aab58050edab3ab44ba868a58