Restructure project directories (#333)

`/client/web` -> `/frontend`
`/client/cli` -> *delete for now*
`/client/native` -> *delete for now*
`/core/editor` -> `/editor`
`/core/document` -> `/graphene`
`/core/renderer` -> `/charcoal`
`/core/proc-macro` -> `/proc-macros` *(now plural)*

frontend/public/site.webmanifest

@@ -0,0 +1,19 @@
+{
+	"name": "",
+	"short_name": "",
+	"icons": [
+		{
+			"src": "/android-chrome-192x192.png",
+			"sizes": "192x192",
+			"type": "image/png"
+		},
+		{
+			"src": "/android-chrome-384x384.png",
+			"sizes": "384x384",
+			"type": "image/png"
+		}
+	],
+	"theme_color": "#f1decd",
+	"background_color": "#f1decd",
+	"display": "standalone"
+}