You'll need to freeze it to make it brittle so you can chip/scrape the thicker stuff. I don't see any snow on the ground in your pics so I'm assuming your in a warm weather climate. If Mother Nature won't freeze it for you, you'll have to use ice or an aerosol freezing agent such as Freeze Spray from Chemtronics. Chip away as much as possible then use a scouring powder like Comet with a hard bristle brush and scrub the whole area. Rinse with clean water and repeat as necessary. There will probably always be a stain there but you should be able to get the worst of it out. This is probably a stupid question, but have you tried getting the contractor to clean this up? I would have to say this is definitely his responsibility.

Oven cleaner will work (after soaking for an hour), but you will need several applications. It will be faster if you heat it up with a torch or heat gun, and wipe off the excess. And yes, this is entirely the contractors responsibility.

I few routes will work You can remelt the tar with a blow torch and scrape it off. The best chemical for dissolving tar is turpentine. Turpentine is in fact a by product from the production of tar from pine sap. No matter what you will probably allways have a stain from it. If all else fails just but a pot plant over it.

Just get over it.