Updated API activities endpoint call per recent API changes
Changed all prior references of 'activities' to 'metrics' for better naming consistency with API
Added new 'activities' request to retrieve activity events (walking, cycling, etc.)
Bodystates have been removed as they are no longer included in the metrics data returned by the API (use activities instead)
Data is now saved to 3 different files (i.e., basis-data-[YYYY-MM_DD]-metrics.json, basis-data-[YYYY-MM_DD]-sleep.json, basis-data-[YYYY-MM_DD]-activities.json)