Valetudo 0.4.0-RE6 preview

Next release for testing RE version, verified on S55 (fw 1898).

The most important change in this release:

• Moved map parsing from server-side to clients.

This way was greatly reduced CPU usage on the device and somewhat lowered RAM consumption.
Also the network bandwidth usage while watching the map was notably reduced as well.

At the same time this change made Valetudo RE incompatible with any third party service that relied on the prepared map data published by the device. Thus the required changes were made for valetudo-mapper companion application: now it can not only create PNG map images but also publish parsed map data in the old compatible JSON format.

As always, I remind everyone the necessity to use valetudo binary with valetudo.conf upstart script from this fork only, as it includes preparations for properly running the service that are missing in the origin script.