Create Progressive Web App (#4730)

* Create manifest and serviceworker

* Create templates and add AppSubUrl

* Add JSRenderer

* fix ctx type

* Add JSRenderer to static.go

* Complete adding {{AppSubUrl}}

* Add more fonts to urlsToCache

* Add 512px and 192px icons

* Hardcode font MD5

* Default theme doesn't have a specific CSS file

routers/routes/routes.go

@@ -791,6 +791,15 @@ func RegisterRoutes(m *macaron.Macaron) {
 		}
 	})
 
+	// Progressive Web App
+	m.Get("/manifest.json", templates.JSONRenderer(), func(ctx *context.Context) {
+		ctx.HTML(200, "pwa/manifest_json")
+	})
+
+	m.Get("/serviceworker.js", templates.JSRenderer(), func(ctx *context.Context) {
+		ctx.HTML(200, "pwa/serviceworker_js")
+	})
+
 	// prometheus metrics endpoint
 	if setting.Metrics.Enabled {
 		c := metrics.NewCollector()