Add MavsdkServer Android lib

[JonasVautherin]

This is the first version of an Android lib dedicated to mavsdk_server.

It can be added to a gradle project with:

implementation 'io.mavsdk:mavsdk-server:0.1.1'

Then, mavsdk_server can be started in the background with something like this:

new Thread(() -> {
  MavsdkServer mavsdkServer = new MavsdkServer();
  mavsdkServer.run("udp://:14540");
}).start();

This is a first version and will be improved in the future.