Refinements to Prairie View metadata loader

[kushalbakshi]

This PR will make the following changes for the current prairieviewreader.py:

• [x] Update internal variable names to be more descriptive of their function.
• [x] Update docstrings within the function and add comments to make the function more readable where appropriate.
• [x] Once above changes are approved, the file name prairieviewreader.py will be changed to prairie_view_loader.py to reflect the file names of the other loaders within element-interface.
• [x] Update CHANGELOG.
• [x] Update version.py.
• [x] Release tag to PyPI after merge.
• [x] Update these lines in scan.py in element-calcium-imaging to reflect the updated file name.
• [x] Update key / value pairs where needed in these lines of scan.py in element-calcium-imaging.

[kabilar]

• [ ] Once above changes are approved, the file name prairieviewreader.py will be changed to prairie_view_loader.py to reflect the file names of the other loaders within element-interface.

Please use git mv to rename this file.