New method to add sites to WeBWorK_Sites

[taniwallach]

The old method to register sites as using WW is no longer functional:

• http://forms.maa.org/r/WebworkSoftware/add.aspx no longer seems to work.
• https://webwork.maa.org/wiki/Instructions_for_registration is focused on how to use that form We should create a new approach.

[drgrice1]

The link to this form is also in the WeBWorK code. See line 3530 of lib/WeBWorK/ContentGenerator/CourseAdmin.pm. That will also need to be fixed.