Documenting additional python imports

[anilyil]

Using an issue to keep track of the additional imports I find throughout the adflow repo:

• The OpenMDAO imports in https://github.com/mdolab/adflow/blob/main/adflow/om_adflow.py and related files will be removed in #196. The new implementation of the OpenMDAO wrappers will only import OpenMDAO if the wrapper itself is imported, instead of importing it any time ADflow is imported.
• Scipy's KDTree is imported in the setDisplacements method in pyADflow
• https://github.com/mdolab/adflow/blob/main/adflow/pyWeightAndBalance.py imports mdo_import_helper (https://github.com/mdolab/adflow/blob/main/adflow/pyWeightAndBalance.py#L38) and pyGeometry_complex (https://github.com/mdolab/adflow/blob/main/adflow/pyWeightAndBalance.py#L43). There are possibly other imports through the `mdo_import_helper' (https://github.com/mdolab/adflow/blob/main/adflow/pyWeightAndBalance.py#L40-L41). This functionality most likely does not work right now.
• https://github.com/mdolab/adflow/blob/main/adflow/pyWingCG.py imports mdo_import_helper similar to the pyWeightAndBalance.py file (https://github.com/mdolab/adflow/blob/main/adflow/pyWingCG.py#L38). Import helper is used to import other stuff. Likely does not work and not used currently.
• https://github.com/mdolab/adflow/blob/main/doc/conf.py imports the sphinx_mdolab_theme to build the documentation (https://github.com/mdolab/adflow/blob/main/doc/conf.py#L1)
• There are several additional imports in the test scripts. I will list them below and include links to one example for each import:
  1. pyGeo https://github.com/mdolab/adflow/blob/main/tests/reg_tests/test_adjoint.py#L11
  2. pySpline https://github.com/mdolab/adflow/blob/main/tests/reg_tests/test_adjoint.py#L12
  3. IDWarp https://github.com/mdolab/adflow/blob/main/tests/reg_tests/test_adjoint.py#L13

[ewu63]

Also, petsc4py is specified as a dependency but actually only PETSc is needed. Same thing happens in IDwarp.