Create the concept of enabled plugins

This allows users to disable a plugin without completely removing it.
Instead, they simply remove the `plugins/enabled/*.bash` file for the
plugin they want to disable.  This continues the concept of "everything
on" while providing greater flexibility to future users.

It might be a good idea to allow turning these off by default in the
future and allowing not only the `plugins/enabled/*.bash` files but also
an array of `<plugin_name>` values that would search for
`plugins/available/<plugin_name>.plugin.bash` to enable them.  That
method would make it easier for people custom tune their plugins from
within their `.bash_profile` script.

plugins/available/nginx.plugins.bash

@@ -0,0 +1,50 @@
+#!/bin/bash
+
+function nginx_reload() {
+  FILE="${NGINX_PATH}/logs/nginx.pid"
+  if [ -e $FILE ]; then
+    echo "Reloading NGINX..."
+    PID=`cat $NGINX_PATH/logs/nginx.pid`
+    sudo kill -HUP $PID
+  else
+    echo "Nginx pid file not found"
+    return 0
+  fi
+}
+
+function nginx_stop() {
+  FILE="${NGINX_PATH}/logs/nginx.pid"
+  if [ -e $FILE ]; then
+    echo "Stopping NGINX..."
+    PID=`cat $NGINX_PATH/logs/nginx.pid`
+    sudo kill -INT $PID
+  else
+    echo "Nginx pid file not found"
+    return 0
+  fi
+}
+
+function nginx_start() {
+  FILE="${NGINX_PATH}/sbin/nginx"
+  if [ -e $FILE ]; then
+    echo "Starting NGINX..."
+    sudo $NGINX_PATH/sbin/nginx
+  else
+    echo "Couldn't start nginx"
+  fi
+}
+
+function nginx_restart() {
+  FILE="${NGINX_PATH}/logs/nginx.pid"
+  if [ -e $FILE ]; then
+    echo "Stopping NGINX..."
+    PID=`cat $NGINX_PATH/logs/nginx.pid`
+    sudo kill -INT $PID
+    sleep 1
+    echo "Starting NGINX..."
+    sudo $NGINX_PATH/sbin/nginx
+  else
+    echo "Nginx pid file not found"
+    return 0
+  fi
+}