Create a 'senses' list and populate

[Owen Carter]

Start with a list of desired capabilities derived from config, either directly (do we have a sensor?) or indirectly (is a pin list defined?)

• eg I2C (and if so; environment, display), pins, network
  Modify this if modules/OS/other config prevent it from being used
• ie; gpio on a non-pi platform; imports not satisfied, device not present, etc..
  Then only initialise and start the services and schedules that are needed. Do not call 'empty' services that will never actually return or act on the data.