Ten sample dialogs, and an update notice

• Ten sample dialogs are written into dialogs/samples/ on first start (a welcome screen, rules, a shop, kits, warps, a player list, a profile, a report form and settings), with /dialog-samples to open a menu of them. samples: false skips them.
• When a newer Dialog Engine is on SpigotMC, the console says so on startup and ops are told when they join. update-check: false turns it off.
• An anonymous usage count: every 30 seconds a random id, how many players are online and the names of plugins that depend on Dialog Engine. telemetry: false turns it off.