Extent update is ignored

[PeterPetrik]

gpkg_contents table contains extent of the data. There are no geopackage triggers to modify extent, but it is done manually by OGR.

ATM we are handling extent conflicts similar to any other conflicts in database, which means sometimes it could lead to invalid extent.

see #29

[wonder-sk]

GeoPackage spec ( http://www.geopackage.org/spec/ ) says:

The bounding box (min_x, min_y, max_x, max_y) provides an informative bounding box of the content. Applications may use this bounding box as the extents of a default view but there are no requirements that this bounding box be exact or represent the minimum bounding box of the content. The values are in the units specified by that CRS.