Verify the split geometries after cutting a simple one link speedlimit
Make the front end speed limit split test harder

Approach is that there is single difficult test case where the speed limit link geometry simulates varying digitization order i.e. the link geometry on some links does not increase towards the next link.
Fix a few coding style issues
Refactor fetching line string features to common place and use it also from unit tests
Merge pull request #339 from finnishtransportagency/improve_frontend_speedlimit_split_test_to_verify_split_geometries

Improve frontend speedlimit split test to verify split geometries