JOcTree Reorganization

[dwfmarchant]

Ok, I started implementing some of the things we talked about this morning:

• Moved the plotting code to JinvVis
• Removed the FEM code
• Deleted create mesh codes that don't work any more (and weren't being included)
• Consolidated numbering functions to one file.
• Consolidated getGrid functions to one file.
• Moved mesh creation codes to separate folder.
• Rearranged JOcTree.jl so it is a bit easier to read.

There are a few things I think we should still do here:

• createOcTreeFromPoints & createOcTreeFromTopo aren't included in JOcTree.jl and I don't think they've been updated. These look useful and they should get cleaned up.
• getLineIntegrationMatrix isn't included in JOcTree.jl and isn't used anywhere. Is this still needed?

[dwfmarchant]

I've also added the codes to read and write UBC format octree files - these were in MaxwellUtils.

[lruthotto]

Shall we merge this or is this still under active development? Without any tests it's difficult to get an overview here.

[dwfmarchant]

Unless there's anything else that we should combine I think we can merge it.