Moved file arguments for Closure Compiler

On Windows I was beginning to hit the command line limit on the size of
the argument string which prevented me from compiling. Closure Compiler will
process any flags passed in through the --flagfile option so I have moved
all the --js file arguments there.
Merge pull request #571 from satsuper/args-fix

Workaround for the command line argument length limit on Windows
Use Qt5 for qtjsruntime
Make qtjsruntime work on windows and it's C:/foo/bar paths
Workaround for DOMParser.parseFromString problem on CI system
Update building instructions