Date on add/edit resource breaks if offset is specified

[icmurray]

This helper function won't parse UTC offset if passed a UTC offset as "+01:00"; but incorrectly parses the UTC offset "+0100" as 100 microseconds.

Resolution:

• I've decided to keep the behaviour of not parsing UTC offsets because we currently don't store timezone information in the database; and I think that either dropping the tzinfo, or adjusting for it would appear to be "magic behaviour" from the user's perspective. Also, as this is a helper function, I think it makes sense to keep the behaviour as is, even if it's slightly non-standard.

This fix [1] maintains all the old non-ISO behaviour:

• not allowing UTC offset to be specified.
• arbitrary delimiters between date and time values.
• microsecond precision.

But won't parse "+0100" as microsecond precision.

I tried using a couple of python modules for parsing date strings; but none maintained the same behaviour.

[1] ​https://github.com/okfn/ckan/commit/d6c9e48f8df5e926abd3fb1a1607f4f5a30075b4