Enable nginx by default, and override the favicon to find the right tab easier

Enable nginx by default since we use it in production and it has broken things before ( https://gitlab.com/gitlab-org/gitlab-ce/issues/27054#note_21914305 )

Was also necessary (easier) to have a GDK-specific favicon for #186

Closes #186

Question: if we should use nginx infront of rails, should rails talk purely over unix-socket? Nginx currently binds on :3443 :3080 (TLS was removed)

doc/prepare.md

@@ -38,7 +38,7 @@ Please read [the prerequisites for all platforms](#prerequisites-for-all-platfor
 ```
 brew tap homebrew/dupes
 brew tap homebrew/versions
-brew install git redis postgresql libiconv icu4c pkg-config cmake nodejs go openssl node npm
+brew install git redis postgresql libiconv icu4c pkg-config cmake nodejs go openssl node npm nginx
 bundle config build.eventmachine --with-cppflags=-I/usr/local/opt/openssl/include
 npm install phantomjs-prebuilt@2.1.12 -g
 ```