make MakeSFTDAG installable as lalapps_MakeSFTDAG

 -moving up contents from MakeSFTs/script directory to MakeSFTs/
 -renaming source python script to lalapps_MakeSFTDAG.py
 -removing executable flag and shebang from it
  since the build system doesn't like it
 -so from now on it needs to be called from install location
  (as 'lalapps_MakeSFTDAG')
  or, if from source tree, as 'python lalapps_MakeSFTDAG.py'
 -refs https://git.ligo.org/CW/lalsuite/issues/35

@karl-wette maybe the main users of this script will actually have issues with those changes, so it's WIP, and maybe you know a more backwards-compatible solution. See CW/lalsuite#35 for details, and except for inline discussions let's keep the conversation focued in one place, i.e. over there?

cc @evan-goetz @gregory.mendell

Closes CW/lalsuite#35