Fix off-by-one error in marker move delay check

This fixes randomly failing integration tests on some machines
Split add asset to layers to addition and assigning visibility
Add markers to layers only when creating new asset
Revert "Remove integration tests from CI build and watch until sporadic errors are resolved"

This reverts commit 0ce174116abcf5acb0032ebf0b32a1910cb953af.
Remove integration tests from CI build and watch until sporadic errors are resolved

This reverts commit 8290c3f8f7df0d566fa372f1d42d8c404bbbd470.
Add test data for linear assets
Take linear asset test data into use in tests
Relay backend object to start function
Remove unnecessary `JOIN` from speed limit import
Construct application model when application is started
Verify that speed limit is drawn on linear assets layer
Style speed limit to 40 kilometers per hour
Support different speed limits
Remove unused code block
Extract script loading to dedicated utility
Use fake linear assets data in fake mode
Add samples of all speed limits to fake data
Create indices for asset link
Add styles for speed limits of 20, 30 and 50 km/h
Return speed limit and side code from api