Support Combined Date and Time

[waylonflinn]

Right now date normalization only works for a very limited set of matching formats.
This should be extended to include time formats, both standalone in a separate column and combined with a date in a single column.

This significantly increases the complexity.

It will likely require:

• Creating formats via combinations of independent date and time formats
• Creation of equivalence classes (several formats should be considered the same)
• Matching specific formats based on input string lengths (limits combinatorial explosion)