add ffmpeg license

reworked licenses into a single generated file

scripts/build-license-html.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+set -e
+
+dir=$(dirname "$(readlink -f "$0")")
+root=$(realpath "$dir/..")
+assets="$root/android/app/src/main/assets"
+
+for filename in "$assets"/licenses/*.txt; do
+    [ -e "$filename" ] || continue
+    moreLicenses="$moreLicenses"'<hr/><pre style="white-space: pre-wrap;">
+'$(cat "$filename")'
+</pre>
+'
+done
+echo "$moreLicenses" > "$assets/moreLicenses"
+
+awk '
+/<\/body>/ {
+    system ( "cat \"'"$assets/moreLicenses"'\"" )
+}
+{ print }
+' "$assets/licenses.html" > "$assets/output.html"
+
+mv "$assets/output.html" "$assets/licenses.html"
+rm "$assets/moreLicenses"