Plugin infrastructure

[tiefpunkt]

Create a standardized interface to plugins. Supports at least two functions:

• Setup
  Setup the plugin. Do the OAuth Dance (see Get access tokens via oauth #6)
• Rung
  do the posting data to somewhere things. Might just get the data, and the core application does the posting. Seems a lot more flexible to me.

Things we need in the core application:

• Configuration storage
  don't think, flat file config will continue to work the way it does right now. might need an intermediate format that can be parsed and written more easily. YAML? JSON?
• Interface
  a proper interface description for plugins
• Data storage provider
  interface to cosm or similar services. maybe also as a plugins? Would just hardcode cosm for now, but we should keep that option open. (Relational database? Google Docs? OpenTSDB?)