When editing / updating a GPKG last_change column in gpkg_contents isn't correctly upheld #168

Describe the bug

A clear and concise description of what the bug is.

To Reproduce

Run the merger on any geopackage to update it. The last_change field won't be updated.

Expected behavior

Either update last_change to be the time of the last write to the table, or to be the data's original creation date.

Additional context

The last_change column as described in geopackage spec:

The last_change SHOULD contain the timestamp of when the content in the referenced table was last updated, in ISO8601 format. Note that since it is not practical to ensure that this value is maintained properly in all cases, this value should be treated as informative.