Optionally hide Monitor page in Admin nav

This adds a new config option that signifies the admin doesn't need to
see deeply technical things, like application resource usage. In the
[app] section, set forest = true to enable this.

Ref T694

config/config.go

@@ -93,6 +93,7 @@ type (
 
 		// Site functionality
 		Chorus        bool `ini:"chorus"`
+		Forest        bool `ini:"forest"` // The admin cares about the forest, not the trees. Hide unnecessary technical info.
 		DisableDrafts bool `ini:"disable_drafts"`
 
 		// Users

templates/user/include/header.tmpl

@@ -104,7 +104,9 @@
 		<a href="/admin/users" {{if eq .Path "/admin/users"}}class="selected"{{end}}>Users</a>
 		<a href="/admin/pages" {{if eq .Path "/admin/pages"}}class="selected"{{end}}>Pages</a>
 		{{end}}
+		{{if not .Forest}}
 		<a href="/admin/monitor" {{if eq .Path "/admin/monitor"}}class="selected"{{end}}>Monitor</a>
+		{{end}}
 	</nav>
 </header>
 {{end}}