Expand usage of PluginContainer.
Remove "replaceable" argument from ServiceManager.
Add a basic implementation of ServiceManager.
Rename Block -> BlockLoc.

* Not confusing for those familiar with MCP names.
* Not confusing for those familiar with Bukkit names.
* Descriptive and short.
Make DataHolder interface for getData() and apply it to BlockLock and Entity.
Add missing package-info files.