Add Fermi PSF convolution method

[ellisowen]

Adds method for fermi energy-dependent psf convolution in gammapy.image.

[cdeil]

I'm not sure if the travis-ci failures are real or a fluke.
Do tests pass for you locally?
Can you add a test and push a new commit to see if the travis-ci tests disappear?

[cdeil]

This function should accept an EnergyDependentTablePSF as input or be a method on that class.

The PSF you use here will only be correct for a given source class and change e.g. when PASS 8 comes out.
Plus we want to use the same PSF class e.g. for HESS and CTA and will need to use those as well.

[ellisowen]

OK, that makes more sense. I will change this.

[ellisowen]

I didn't notice the errors before, but I get a lot now (I was originally going to make one pull request but then separated the commits out, so I probably screwed something up then). They all seem to relate to FermiGalacticCenter though, which isn't changed here:

I'll try and fix this and make a pull request if there's some kind of bug

e.g. here's an error message:

______________________________________ ERROR collecting gammapy/irf/tests/test_effective_area.py _______________________________________
gammapy/irf/tests/test_effective_area.py:10: in

from ...datasets import arf_fits_table
gammapy/datasets/init.py:5: in
from .load import *
gammapy/datasets/load.py:25: in
from ..spectral_cube import GammaSpectralCube
gammapy/spectral_cube/init.py:5: in
from .core import *
gammapy/spectral_cube/core.py:23: in
from ..image.utils import coordinates
gammapy/image/init.py:3: in
from .healpix import *
gammapy/image/healpix.py:11: in
from .utils import coordinates
gammapy/image/utils.py:11: in
from ..datasets import FermiGalacticCenter
E ImportError: cannot import name FermiGalacticCenter

[ellisowen]

Made changes, new pull request as implementation changed quite a bit: see #155