Fix erroneous or obsolete dateloc values in yields table and normalize date values.

[gsrohde]

The permissible dateloc values are now limited to 5, 6, 7, 8, 9, 95, 96, and 97 (and possibly 5.5).

For each dateloc value other than 5, there are now prescribed values for year, month, and day for use in representing indeterminate information.

The script https://github.com/PecanProject/bety-qaqc/blob/master/date_time_cleanup/Yield_dates_fix_script.sql comprises my proposed procedure for dealing with anomalous representations of yield dates.

@dlebauer, @robkooper I'd like another set of eyes on this before I go ahead with the cleanup.

[dlebauer]

Looks good. Go for it. Please post results of select statements here

[dlebauer]

Also, make a dump of the yeilds id and date fields before executing the script for reference

[gsrohde]

@dlebauer I did most the cleanup on yields date/dateloc values. All dateloc values are now in the set 9, 8, 7, 6, 5.5, 5, 97, 96, 95.

The attached file shows remaining problematic cases--rows where the specificity of the date value suggests that the dateloc value is wrong.
problematic_yields_date_information.txt