Updated installguide
  - added more required packages to the "apt-get install"-list
  - removed the note about modifying paths in code --- no longer necessary
Moved backup-logic to server-side
  - send XML and animation JSON in same "save"
  - keep logic wrt. backup numbers inside BackupSys
  - base "current backup number" on presence of existing backup files rather
    than contents of separate "num"-file