Bugfix 1173: Correctly apply sortedness checks when calling update with date_range argument

[alexowens90]

Closes #1173

Also:

• Set the sortedness field to UNKNOWN for all non-timestamp indexed dataframes. Previously, this would be set to ASCENDING/DESCENDING for int/range indexes based on the DataFrame.is_monotonic_<in|de>creasing of the input df, but this information was not used for anything
• Fixes the docstring of the returned dict from NativeVersionStore.get_info to include the sorted key
• Add the sorted field to the SymbolDescription class returned from Library.get_info
• Simplifies and extends the tests for sortedness checks with update