Upgrade version numbers to match Play 2.3.1, etc

Also:
- Change from play.Project to Project
- Upgrade Specs from 1.14 to 2.3.12, since 1.14 apparently isn't
  available for Scala 2.11.
- Remove this: (`playOnStopped/Started` are gone?)
    playOnStarted += startGulpTask,
    playOnStopped += stopGulpTask
Comment out SecureSocial, upgrade/replace S.S. later

This breaks Facebook login, until S.S. included again.  Remove SecureSocial
plugins, for now, in conf/play.plugins.
Rename SimpleResult to Result, since Play renamed it.
Change from Option[Any] to Unit, import execution context

Apparently empty body type changed in Play 2.3.
Place compiled JS in scala-2.11/ not -2.10, else not found.
Comment out OpenID login. OpenID lib no longer found, no idea why.
Fix compilation error: Rename PageRequest.apply() to .basedOnApiRequest().
Fix path to favicon.
Add -jvm-debug to Activator scripts, rename.
Barely make Silhouette Facebook login work, work in progress.
Delete submodule SecureSocial.
Tidy up login code, use correct auth callback origin

And remove some unused login related code.
Actually login and save logins in database, Facebook only.
Remove SecureSocial controller, rename Silhouette to OpenAuth.
Make Google login work, and the login popup.
Remove no longer needed Play plugins file.
Use None not '' if email absent, breaks tests, I'll fix later.
Change OAuth callback to /-/login-auth-callback/:provider.
Add Twitter and GitHub login, disable Yahoo since OpenID broken

OpenID broken after upgrade to Play 2.3.
Login with OAuth via debiki.loginOrigin

If logging in via OAuth at site X, then redirect to debiki.loginOrigin
and login from that site instead, because the OAuth redirect_uri
supposedly points to debiki.loginOrigin. Then redirect back to the
original site, with the session id and an XSRF token, and continue.