Some cleanup and updates on the CI, including:
* creating a common docker image for all jobs
* expose test failure report to merge requests

also:
* add h5 output tests
* use debian sphinx packages instead of pip

implement as __main__ for `gwinc.ifo`

also add to CI.  closes #48

Drop specific comparison to MATGWINC output and move to comparisons to
cached hdf5 traces.  Comparisons to all cached IFO traces will be done by
default.  A PDF report of all discrepancies for all IFOs will be
generated if requested.  inspiral ranges will be calculated if the
inspiral_range package is available.

This adds trace caches (in git-lfs) for all currently supported IFOs,
effectively snap-shotting the current state of the repo.

gitlab CI also updated to use new tests

This patch provides a new nb sub-module that defines classes for managing
and calculating noise budgets.  It provides the following overridable
classes:

nb.Calibration  A noise calibration
nb.Noise        A noise source
nb.Budget       A budget of noises

The Budget class includes a calc_trace() method that will return a traces
dictionary that includes data and trace plot styling for every noise term
in the budget recursively.

The existing included interferometers are updated to define their budgets
using this new interface, and the plot_noises function is updated to
accept the new traces dictionary.

An HDF5_SCHEMA describes how trace dictionaries are encoded into HDF5 files.
The new io module includes functions for writing traces to HDF5 files, and
for reading traces stored in this format.

The command line interface is updated to handle this new structure.

With this tweak, most noises agree within 1 ppb.  Exceptions are
seismic and substrate TE (which still have open bugs in matgwinc).

Arguments added to gwinc.test for setting a tolerance level, and a
list of noises to skip in the comparison.

The CI pipeline will now fail when tests fail.

and move to python3

Error is:

  jobs:test:cache:key config cannot contain the "/" character

addresses #2