fix: Move content into to frontend directory

Doing this BEFORE the merge prevents a lot of merge conflicts.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

frontend/public/icons/browserconfig.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<browserconfig>
+    <msapplication>
+        <tile>
+            <square150x150logo src="/icons/mstile-150x150.png"/>
+            <TileColor>#b51f08</TileColor>
+        </tile>
+    </msapplication>
+</browserconfig>

frontend/public/icons/site.webmanifest

@@ -0,0 +1,18 @@
+{
+    "name": "HedgeDoc",
+    "short_name": "HedgeDoc",
+    "icons": [
+        {
+            "src": "/icons/android-chrome-192x192.png",
+            "sizes": "192x192",
+            "type": "image/png"
+        },
+        {
+            "src": "/icons/android-chrome-512x512.png",
+            "sizes": "512x512",
+            "type": "image/png"
+        }
+    ],
+    "theme_color": "#b51f08",
+    "background_color": "#303030"
+}