Time cadence sync when combining dfs

[tinsmcl1]

Sync dataframes when cadences differ (e.g. set AB is every hour but set C every minute)

Functionality for combining dataframes:

• We can keep only the times in AB
• We can keep only the times in C
• We can keep all data points from all sets (may result in many incomplete rows)
  - Future consideration: We can interpolate the missing data to form a complete dataset