- Move most of the contents of DeconvolveHybridM into
DeconvolveHybridMBase.

- Create subclasses that enable the user to deconvolve either the
driftscan analytical beam model or an external beam model.

- Create subclasses that enable a Tikhonov scheme for deconvolution
that uses a single regularisation parameter, or Weiner scheme that
assumes some model for the m-mode power spectrum of the signal.

- DeconvolveHybridMBase now computes the el-dependent EW dirty beam
and saves it to the output RingMap container if requested.

- DeconvolveHybridMBase now normalizes by the el-dependent
peak of the dirty beam so that point source peak flux is
preserved through the map making process.

- Create beam.py module and CreateBeamStream task that takes a
CommonModeGridBeam container and converts it to a HybridVisStream
container that can be m-mode transformed and used in the
deconvolving ringmapmakers.

- Add an el axis to the weight dataset in the RingMap container,
since the noise after deconvolution will be el dependent.

- Propagate noise variance through the deconvolution process.
Create RADependentWeight task that re-introduces the RA dependence
to the weights that was lost in the round-trip m-mode transform.
Applying this procedure to Gaussian noise realizations recovers
the standard deviation of the noise at the <10% level.

This also makes dirty_beam an optional dataset of HybridVisStream.

Use the model suggested by Dallas for the signal power spectrum
in the Wiener ring map maker. The model spectrum has contributions from
galactic synchrotron and extragalactic point source emission.  The
galactic emission has a power-law dependence on both m and frequency.
The point source emission has a power-law dependence on frequency only.
Set the default parameters to those suggested by Dallas.

Add the capability to DeconvolveHybridMBase to apply a window
to the deconvolved m-mode transform of the ringmap.  This can
be used to shape the synthesized beam in the EW direction.
Provides an option to use the same window for all frequencies
to try to produce a frequency-independent synthesized beam.