Fix the URL for initiating a JSConnect Sign In when using V3.

[nervoustwit]

This will close vanilla/support#1864

When we do not use JSConnect as the default method of signing in, we have the JSConnect button link directly to the endpoint that creates the JWT to be sent to the Authentication provider. When it is the default method, we don't do that. This causes inconsistencies in the way some customers have coded their applications to handle JSConnect.

This PR will make sure that all the links to sign in pass through the /entry/jsconnect-redirect endpoint.

Testing

• Configure JSConnect for v3
• Make it the default method for logging in.
  • Click to log in, make sure it goes through /entry/jsconnect-redirect
  • Turn on private communities, access the site, make sure it goes through /entry/jsconnect-redirect
• Make JSConnect NOT your default method, make sure it goes through /entry/jsconnect-redirect
• Repeat all the above steps with V2 to make sure we haven't broken backwards compatability.