Change morphology model input format

[cdeil]

This is a reminder issue that I'm assigning to myself.

I'd like to change the morphology model input format a little, pretty much to what I did for spectra here: #119

So this:

pos:
  glon: {val: 332.391d, err: 0.014d}
  glat: {val: 0.138d, err: 0.013d}

morph:
  type: gauss
  sigma: {val: 0.136d, err: 0.008d}

would change to this:

morph:
  model:
    type: gauss
    parameters:
      glon: {val: 332.391d, err: 0.014d}
      glat: {val: 0.138d, err: 0.013d}
      sigma: {val: 0.136d, err: 0.008d}
  # could have other info about the measurement here

This requires an hour or two of tedious input data reformatting, but also changes to the spec, scripts, possibly output format and Gammapy, so I'd like to do it myself.