Update btsync build :
 - Move data directory from /btsync_data to /data to be consistent with my others projects
 - Create volume /data by default
 - move btsync port from 27027 to 1337, expose it by default and it can't be change with env var anymore
 - Remove useless helper
Update make file : tag images with lastest and a date and git based tag (date.githash)