Fix Social Account Block

If you have omniauth enabled, but don't have one of the "Social" providers enabled (GitHub, Twitter, Google), the "Social Accounts" sections shows up, but without icons. This occurred when I was testing Shibboleth. This fixes the issues by checking if there are any `enabled_oauth_providers` rather than if just `Gitlab.config.omniauth.enabled`. Not quite sure how to implement a test for this, but it works :).