Add command script containers

All command scripts will be forcibly registered with CraftBukkit. Cannot
guarantee stability on non-CraftBukkit-based servers.
Add context to command script containers

This is probably needed.
Update CommandScriptContainer.java
Force servers to use Bukkit's /help command instead of Mojang's

Only if they're using Mojang's though.
I'm not quite sure why there's two versions of the command, but it seems
that it'd be really annoying for /? to show commands, but /help not...
Also added a help viewer script thing that @mcmonkey4eva can document
better :smile_cat:
[ProofOfConcept] Add item_message mechanism to dPlayers

This isn't really the cleanest thing ever, but it does work, and it can
be used for various purposes.
Merge pull request #843 from Morphan1/master

My commands are registered!
Merge branch 'master' of https://github.com/aufdemrand/Denizen