Second beta release for cpdb-backend-cups 2.0.0

• Return printer list upon activation and subscribe to cups for updates (PR return printer list upon activation & subsrcibe to cups for updates #20)
  • Return printer list synchronously upon activation
  • Subscribe to CUPS notifications for printer updates
  • Automatically update frontends about new printers found, old printers lost, or printer state changed
• Added the support of cpdb-libs for translations
  • Using general message string catalogs from CUPS and also message string catalogs from individual print queues/IPP printers.
  • Message catalog management done by libcupsfilters 2.x, via the cfCatalog...() API functions (catalog.h).
• Option group support
• Added billing-info option (PR add billing-info option #19)
• Log messages handled by frontend
• Use pkg-config variables instead of hardcoded paths (PR use pkg-config variables instead of hardcoded paths #17)
• Build system: Let make dist also create .tar.bz2 and .tar.xz