allow introspection of providers

[mmerickel]

It might be useful to see a list of configured providers in an application. This should be done using Pyramid's 1.3+ introspection API.

There is also an outstanding question of whether the list of providers should be introspectable via a URL in the standalone application. I'm having difficulty seeing why this would be useful because it is entirely specific to velruse.

[kiorky]

#47 (comment) for reference .... how to waste time ...

[kiorky]

Its maybe because velruse is not the endpoint (my use case was my apex fork needing some bit of velruse information like knowing which providers it would enable (google, facebook, ldap, etc))

[kiorky]

And also #52 (comment)