Add missing modules to init.py

[kandersolar]

• Closes #xxxx
• I am familiar with the contributing guidelines
• Tests added
• Updates entries to docs/sphinx/source/api.rst for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels and Milestone are assigned to the Pull Request and linked Issue.

__init__.py is missing several modules. Some of the omissions don't make a practical difference, maybe because they get imported by other modules. For shading and scaling, some import patterns fail:

$ python -c 'from pvlib import shading'  # works; this is how the test suite does it
$ python -c 'import pvlib; pvlib.shading'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AttributeError: module 'pvlib' has no attribute 'shading'

I think I got all the missing modules but another pair of eyes never hurts.

[wholmgren]

Ah good catch @kanderso-nrel. Putting the imports in alphabetical order would make it easier to catch missing modules. While you're at it, I think this pattern might be more concise:

from pvlib import (  # noqa: F401
    shading,
    snow,
)

[wholmgren]

ignoring psm3 failures and merging... thanks @kanderso-nrel