Add new emacs-gui-server and emacs-gui-client commands

The idea behind these commands is to easily launch a Emacs server which
runs in the background, but with font/theme/etc settings as if it was
launched like a normal GUI.

I used to just launch Emacs.app directly, but, now I use these binaries
to open a full GUI frame by executing `emacs-gui-client -c &`. After
starting the GUI server with `emacs-gui-server start` of course.

The main difference between calling `emacs --daemon` and
`emacs-gui-server start` is that the latter uses a custom socket as to
not interfere with any console-base Emacs server, and it also sets the
`EMACS_GUI_SERVER` environment variable to `1`, letting my Emacs config
figure out which theme/fonts/etc to load.

bin/emacs-gui-client

@@ -0,0 +1,15 @@
+#! /bin/bash
+
+# Defaults
+SOCKET_DIR="$TMPDIR/emacs-gui-server$(id -u)"
+SOCKET_FILE="$SOCKET_DIR/server"
+EMACSCLIENT="emacsclient"
+ALTERNATE_EDITOR="nano"
+
+# Set to binary bundled in Emacs.app if it exists
+if [ -f "/Applications/Emacs.app/Contents/MacOS/bin/emacsclient" ]; then
+  EMACSCLIENT="/Applications/Emacs.app/Contents/MacOS/bin/emacsclient"
+fi
+
+# Execute emacsclient
+exec $EMACSCLIENT -s "$SOCKET_FILE" --alternate-editor=$ALTERNATE_EDITOR "$@"