Restructuring of sketch for better maintainability

- Added a system state machine so transitions are easier to follow
- Refactored translateToOz so it is easier to maintain, changed name to
  translateFlexiforceToOz
- Added "Flexiforce" to functions that are specific to that sensor
- Battery reading is taken in main loop instead of pressure reading
- Main loop now also samples accelerometer and temperature, but the
  values are not yet used