Remove dependence on static singleton Instance of SisbaseBot #46

In particular, the areas where SisbaseBot.Instance are currently used are the SMC (being the legacy code that it is), and to access Sisbase infrastructure from commands (which belong to D#+.CommandsNext, and currently have no way to access the bot).

• The conversion of SMC to a property on each bot instance should be fairly trivial
• Accessing the "active" sisbase instance from within a command may be harder
  • currently, we are investigating CommandsNext dependency injection as a way to deliver the instance to the command, but it's possible that if D#+ doesn't allow a way to avoid boilerplate while doing this, we will reject that solution and have to find something else. Boilerplate is unacceptable.