- Add 'too_hot_flag' to indicate whether watering is required because
  soil temperature has exceeded CropEvent limit.
- Fix CropSeason.delete_orphan_events to properly handle all=True.
- Convert probe temperature readings from Celcius to Farenheit.
- Enforce temperature sanity checks using Farenheit.
- When 'do_not_irrigate' flag is present, don't set 'check_probe_flag'
  or 'too_hot_flag'.
Minor logic change, no functional difference.
- Add max allowed and max observed temperature columns.
- Add a new 'header' row to separate water and temperature sections.
- Show red themometer icon when watering is required because observed
  temperature exceeds temperture limit.
Add 'do_not_irrigate' field to CropEvent admin pages.
Change logic for extracting data from the UGA probe reading database.
The script iterates across all probe_reading records (in date/time
order).
Old algorithm:
- A single record was created for each date + probe_id
- Only entries between 1am and 9am were processed, other
  entries were ignored.
- Later probe_reading entries on the same date overwrote any data
  stored in the the record.
New algorithm:
- A single record is created for each date + probe_id.
- For entries between 1am and 9am: all information *except* 2in soil
  temperature readings overwites existing date in the record.
- The maximum observed 2in soil temperature readings are stored in the
  record.
Add WaterRegister.too_hot_flag to database
Color code WaterRegister page, past:grey text, present:yellow background, future:greener background