Plex+Tree: small fixes to DMPlexComputeInterpolatorTree()

WIP: DMPlexComputeInterpolatorTree()

Forest: Add an HDF5 viewer

DMP4est: added childIds to GetTranserSF_Internal

This will let me figure out which parts of the reference tree's
constraint matrix to use.

DMP4est: Added DMPlexReferenceTreeGetChildSymmetry_p4est()

This is needed to match up dofs when constructing
interpolation/injection.

DMP4est: move string declarations to function boilerplate

DMP4est: use a custom reference tree

DMP4est: started DMCreateReferenceTree_p4est()

This will simplify intergrid transfer.

DMP4est: added bare-bones DMCoarsen_p4est()

This just gets a reference to the coarseDM. We need to figure out the
control flow for on-the-fly adaptive coarsening.

DMP4est: introduce command line refinement options

TODO: make them accessible via functions.

Forest: Added simple viewer for pest

DMP4est: pass periodicity

DMForest: initialize more header functions when cloning

DMP4est/DMPlex: Share DMSNES/DMTS information when converting

This includes "A", "dmAux" and "dmCh" for now.

DMComputeL2FieldDiff(): fixes, DMP4EST implementation

DMForest: Add specific Clone for pest

DMP4est: revamp operating without a base DM

- Construct a ghost label in this case
- Make reading a brick connectivity more full featured

DMP4est: fix label/ghost interaction with internal plex representation

We have to create labels for the internal plex, construct the ghost
cells, and then copy the labels back from the ghosted plex.

DMP4est: add Vec viewers and loaders via plex

These can be replaced with p4est native vtk routines if need be, but
that would require my digging into the layout of dofs to vertices,
cells, etc., whi

DMP4est: add Vec viewers and loaders via plex

These can be replaced with p4est native vtk routines if need be, but
that would require my digging into the layout of dofs to vertices,
cells, etc., which I don't want to do right now.

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DMP4est: cleanup

DMP4est: also share value map in DMShareDiscretization()

DMP4est: stop using DMPlex to get global vectors.

It creates confusion in VecGetDM(), and it's only advantage right now is
the ability to piggyback off of the VecView*() routines that plex
implement

DMP4est: stop using DMPlex to get global vectors.

It creates confusion in VecGetDM(), and it's only advantage right now is
the ability to piggyback off of the VecView*() routines that plex
implements. We can put those back in later if needed.

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DMP4est: share point sf of ghosted plex back to p4est

Even though the ghosted cells aren't really present for the p4est, right
now all numbering has to coordinate between the two.

DMP4est: share application context with ghosted plex

In ts ex11, I now have to address the fact that there is plex specific
stuff in SetInitialCondition(). Work on that tomorrow.

DMP4est: use DMLabelGetValue, since this doesn't need to build the index