Change bot commands to be modular and dynamically changable

[mellowagain]

At the moment bot commands are highly integrated into Shiro itself and allow for no flexibility. If one wants to change a command, re-compilation and re-linking of Shiro as well as a full restart of the running server is required.

I propose the following things:

• Separate commands out of Shiro into separate modules.
• Allow dynamic loading and unloading of these modules.

We may also in the future allow extension of these by using in-program scripting using a Python or Lua embedded runtime with our own API.