#RFC: Updated spectralnorm.jl for ~30x speedup

The previous version based on Scala ran in just under 5 minutes (~293s), while this version,
based on Javascript with tweaks, runs consistently in 10-12s. This puts Julia ahead of all
other dynamic languages and only behind C/Ada/Fortran using extremely low-level and in some
cases parallelization (which maybe we should explore). Julia FTW!
Let me know if we can make any other tweaks/optimizations. 
Merge pull request #2806 from karbarcca/patch-2

Updated spectralnorm.jl for ~30x speedup