web: stylize the file receiver, move text to i18n, update remux page

web/i18n/en/receiver.json

@@ -0,0 +1,5 @@
+{
+    "title": "drag or select a file",
+    "title.drop": "drop the file here!",
+    "accept": "supported formats: {{ formats }}."
+}

web/i18n/en/remux.json

@@ -0,0 +1,3 @@
+{
+    "description": "remuxing media files is fast, lossless, and often fixes compatibility issues with old software. files are processed on-device and never get uploaded anywhere."
+}