Anbangx/find start seed min length

@jakebiesinger @JavierJia @Elmira88 @Nan-Zhang 

This PR is for findMinScaffoldingMinLength, which separates the setCutoffCoverage and findMinScaffoldingMinLength from the previous PR I sent. hpc is broken, I need more time to test that Gaussian model in the real data. So this PR can be used to get startSeed first.