Consider more guidance and informative error msg for combined species without full time-series support

[AdamCSmithCWS]

Some help documentation and informative warnings would be useful to help users understand the complexity of time-series information for some of the lumped and split species' complexes.

1. Alternative start dates for

• Traill's Flycatcher complex,
• Eurasian Collared Dove, Cave Swallow, and others that were missing from the survey for the first ~10 years

2. Warning messages for Meadowlarks etc, where the ability to separate species or forms may have gotten worse with time (most get better)