Full player backups/rollbacks on demand

As referenced from #60, a way to completely back up & roll back players on demand, with additional configuration to automatically rollback on death. Could mostly reuse code from the player reset module.

[Eluinhost]

Though technically possible I'm not sure it's too great an idea. The player reset is only intended to be an 'oh shit' quick rollback after a short duration and importantly is an automatic 'backup' after those commands. Having to manually backup/restore seems to be of limited actual use (and would probably also require location storage and maybe more like respawning if dead). Keeping the itemstacks e.t.c. in memory for extended times beyond the usual undo timer could cause other problems too.

As for limited actual use, I personally use my own /rollback a lot of times during games (helps to check if people died to a glitch/their own fault), but I can see the potential issues of keeping so much data in memory.

For locations Bukkit actually stores the World object so I can also see where a memory leak argument could come from (especially under multiworld setups). Maybe move to 1.2 milestone?

[Eluinhost]

Either as 1.2 or as a separate plugin. I'll leave this ticket open for the time being