Enable global side/mobile menu in config

fix #194

Author: gkorland

_config.yml

@@ -18,6 +18,9 @@ aux_links:
 # Makes Aux links open in a new tab. Default is false
 aux_links_new_tab: true
 
+# Enable the side/mobile menu globally
+nav_enabled: true
+
 plugins:
   - jekyll-sitemap
   - jekyll-redirect-from