Code refactoring for #1141

Closes #1141 (closed)

gpaw.spline.Spline()
Updated signature

gpaw.spline.Spline.from_data()
Migrated from old instatiator

gpaw.spline.Spline.{l|_npoints}
Now a property

gpaw.spline.Spline.get_npoints()
New method

gpaw/ae.py
gpaw/ah.py
gpaw/atom/radialgd.py
gpaw/calculator.py
gpaw/core/atom_centered_functions.py
gpaw/densities.py
gpaw/ffbt.py
gpaw/lcao/bsse.py
gpaw/lcao/overlap.py
gpaw/lfc.py
gpaw/new/tb/builder.py
gpaw/pseudopotential.py
gpaw/response/paw.py
gpaw/sphere/integrate.py
<Various tests>
Refactored to be compatible with the new signature of Spline