Would it be viable to use jet blast deflectors as a power source?
From an environmental point of view would installation of windmills just before jet blast deflectors provide enough power to power up all machinery at airports?


From an environmental point of view? Not sure what that has to do with providing power, but no, here's why: First, many airports do not have jet blast deflectors at the ends of runways or in a place that sees most of the jet blast. 

Aside from that, windmills (wind turbines) can't spin at unlimited speed. Here's what happens one one goes too fast (small turbines have the same issue, but can stand wind speeds up to 100-ish mph). Turbines are designed such that they have an optimal output within some speed range, below that they don't generate much power, and above that they can get hot and fail, or have to be throttled back to stay in the power band. 

So seeing as how you would need to have them close to the ground where they aren't useful for natural breeze, providing major power to the airport is not going to happen. 


  How much of a reduction in reliance on fossil fuel sources of energy would that be?


Why do you assume that the airport runs on fossil fuels? Many airports are running "green" initiatives, installing solar panels and bio-diesel reactors. They may also be purchasing renewable energy credits so that they try to get a good portion of the power used from renewable sources, such as wind farms. 


  By how much would that reduce landing fees and could the energy provided at least power a mechanism that could tow All aircraft (including the Airbus A380 and the Boeing 747) during the entire taxi phase pre flight and post landing along with ALL airport machinery in busy airports like Heathrow


Such a tow system would almost undoubtedly increase landing fees. You are looking at it purely from a fuel savings view, but lets look at it from other angles:


Cost: There would be an extremely high acquisition cost, all the taxiways would have to be reworked to include this system. Even if it were an autonomous tow vehicles, the structure is not free. The tow's have to be created, programmed, vetted, certified, etc. 
Maintenance: There is a lot of infrastructure to maintain, the tow vehicles, the electronic systems, mechanical systems, etc. This requires a full-time crew, and I'm sure they aren't going to work for free, plus enough on-hand spares to be able to quickly repair the system when it goes down. 
Logistics: You have to have the tow mechanisms in place to catch the aircraft as they come off the runway. This means enough tow mechanisms to tow all aircraft and transit back to the runway possibly empty to catch another aircraft. 
Other issues... Aircraft can't just shut down engines right after they land. Many engines have cool-down times before they can be shut down. They also can't just fire them up at the end of the runway, there are start-up times and warm-up periods. Aircraft also need to power systems on the way to the runway, air conditioning, avionics, hydraulics, etc.


Honestly these tow systems are not economically viable at this time. Aircraft are extremely fuel efficient (although not on the ground), but they have procedures to mitigate fuel expense on the ground. They shut down unused engines, turn off anything that isn't required, and reduce power consumption. 

If you are looking for ways for the airport to save energy or generate it themselves, then solar panels or these tiles that generate electricity are more viable.