Speed averages (year and year-quarter grains)

[tiffanychu90]

segment speeds

• refactor average_segment_speeds and average_summary_speeds script for clarity, extended uses, and more generalizability:
  • use the same function for single day or multi-day averages
  • allow weighted averages for peak/offpeak/all_day calculations (which changes the grain and stacks the time periods as extra rows) or simple averages (aggregated at the grain it is at)
• since the segment geometry is fairly stable across time, start averaging speeds over longer time spans to get a quarter (year-quarter) and year grain and test results for stop_segments
• add more entries into gtfs_analytics_data.yml to explicitly define which columns are ones to group over and allow various grouping columns
• note that the stop_segments.shape_stop_singleday entry could be deprecated or swapped out to support time-of-day averages - do a little exploratory work to decide
• Research Request - Segment stability in speed time-series #1202