Add project official docker image.

Tag for docker image is set from project version.
To build docker image for the project run:
- mvn package
- mvn -N dockerfile:build

Created docker image can be uploaded to the docker hub:
- mvn -N dockerfile:push

Signed-off-by: Yahor Berdnikau <egorr.berd@gmail.com>

dockerfiles/run.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+mkdir -p $AIRSONIC_DIR/data/transcode
+ln -s /usr/bin/ffmpeg $AIRSONIC_DIR/data/transcode/ffmpeg
+ln -s /usr/bin/lame $AIRSONIC_DIR/data/transcode/lame
+
+chown -R $UID:$GID $AIRSONIC_DIR/data $AIRSONIC_DIR/playlists $AIRSONIC_DIR/podcasts
+
+exec su-exec $UID:$GID tini -- \
+     java -Xmx256m \
+     -Dserver.host=0.0.0.0 \
+     -Dserver.port=$AIRSONIC_PORT \
+     -Dserver.contextPath=/ \
+     -Dairsonic.home=$AIRSONIC_DIR/data \
+     -Dairsonic.defaultMusicFolder=$AIRSONIC_DIR/musics \
+     -Dairsonic.defaultPodcastFolder=$AIRSONIC_DIR/podcasts \
+     -Dairsonic.defaultPlaylistFolder=$AIRSONIC_DIR/playlists \
+     -Djava.awt.headless=true \
+     -jar airsonic.war