Command blocks

I am currently working on Command Blocks (with >1.8 functionality). This is to track the progress of these branches: [API](https://github.com/GlowstoneMC/Glowkit/tree/command-blocks-api) & [Server implementation](https://github.com/GlowstoneMC/Glowstone/tree/command-blocks).

**To-Do**:
- [ ] Update the Command block API for the new functions
- [ ] Place the new command blocks
- [ ] Save TileEntity and MaterialData for command blocks
- [ ] _Incomplete_ Open command blocks when clicked
- [ ] Save data when closed
- [ ] Fix a bug with duplicate interaction packets (opening the command block twice)
- [ ] _Incomplete_ Use op permission levels
- [ ] Set permission level when joining the server (EntityStatus)
- [ ] Add permission level to configuration
- [ ] Make command blocks reactive to redstone
- [ ] Execute commands on behalf of the block
- [ ] Chain command blocks

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Review the command-blocks-api branch and the command-blocks server branch first. Use the checklist to scope the work across placement, TileEntity and MaterialData persistence, interaction and permission handling, redstone activation, command execution, and chaining. Done means the listed command-block functionality is implemented and the incomplete items are resolved.

Written by the indexing model from the issue text.