change default of COMMON_ENABLE_BASIC_AUTH to False

I changed the default behavior of basic authorization to false.  I found the default behavior unintuitive.  Upon installation of the default image via vagrant, going to the server from a remote host (including the vagrant host computer) prompts the user for a username/password.  The default behavior should be that the edx lms/cms "just work" without a username/password, right?  Furthermore, the documentation does not mention that the username/password is edx/edx, and one can only find this information by going into the source files.  Finally, I didn't see a great reason to use basic auth at all, and thus if someone wants to use it, they probably should explicitly enable it, instead of this being the default behavior.
alright, see pull #1286