Shallow_flash.bat makes it easy to flash on windows + cygwin

This attempts to make it easy to to shallow flash on Windows as many windows users are not very technical and are likely to get confused with cygwin paths etc. 

The idea is you just install cygwin (and unzip), copy adb, fastboot, gaia and gecko to the same foldr as this shallow_flash.bat and double click it.

I also removed the unnecessary lines in shallow_flash.sh for the windows hack