Move empyscripts into empymod.scripts

Merge empyscripts into empymod under empymod.scripts.

• Clear separation between mandatory and optional imports:

  • Mandatory:

    • numpy
    • scipy

  • Optional:

    • numexpr (for empymod.kernel)
    • matplotlib (for empymod.scripts.fdesign)
    • IPython (for empymod.scripts.printinfo)

• Broaden namespace of empymod. All public functions from the various modules and the modules from empymod.scripts are now available under empymod directly.