This removes all uses of both `send` and `public_send` from consumers of
SiteSetting and instead introduces a `get` helper for dynamic lookup
This leads to much cleaner and safer code long term as we are always explicit
to test that a site setting is really there before sending an arbitrary
string to the class
It also removes a couple of risky stubs from the auth provider test
Previously we relied on the provider name matching the name of the icon. Now icon names are explicitly set. Plugin providers which do not define an icon will get the default "sign-in-alt" icon
At the moment core providers are hard-coded in Javascript, and plugin providers get added to the JS payload at compile time. This refactor means that we only ship enabled providers to the client.
Sam Saffron
David Taylor
Leo McArdle