Fix F-Droid bot feedback issues [skip ci]

- Move fastlane metadata to repository root (was in android/fastlane)
- Add distributionSha256Sum to gradle-wrapper.properties for security
- Update Gradle Wrapper JAR to match version 8.13
- Document NonFreeNet anti-feature (HTTP support for local WebDAV servers)

Addresses F-Droid RFP issue #3458 bot feedback

android/gradlew

@@ -1,7 +1,7 @@
 #!/bin/sh
 
 #
-# Copyright © 2015 the original authors.
+# Copyright © 2015-2021 the original authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -114,7 +114,7 @@ case "$( uname )" in                #(
   NONSTOP* )        nonstop=true ;;
 esac
 
-CLASSPATH="\\\"\\\""
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
 
 
 # Determine the Java command to use to start the JVM.
@@ -213,7 +213,7 @@ DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
 set -- \
         "-Dorg.gradle.appname=$APP_BASE_NAME" \
         -classpath "$CLASSPATH" \
-        -jar "$APP_HOME/gradle/wrapper/gradle-wrapper.jar" \
+        org.gradle.wrapper.GradleWrapperMain \
         "$@"
 
 # Stop when "xargs" is not available.