[importer] Refactor import result notification
CDB-290 #resolve [importer] Report to GitHub unknown errors only
clean up
CDB-294 #resolve [importer] Raise KmlNetworkLinkError when importing a KML with just a link to the actual data
CDB-300 #resolve [importer] Raise InvalidGeoJSONError when invalid .geojson
[importer] fix specs
CDB-306 #resolve [importer] Raise InvalidShpError when no .dbf or .shx
Report general import failure to Rollbar
[importer] Update shp2pgsql spec
CDB-299 #resolve [importer] Provide error description for ShpNormalizationError
CDB-308 #resolve [importer] Raise if resulting the_geom is a GEOMETRYCOLLECTION
Merge branch 'importer2.2' into release/staging