Added `GridFile` helper to automate grid file output

[WillJRoper]

This PR introduces a GridFile IO helper class. This class:

• Automates common HDF5 processes.
• Provides an interface to automate the writing of datasets with descriptions and units in a succinct way and attribute writing.
• Automates opening and closing.
• Provides a helper method to simply write out all grid attributes and datasets common between all models.
• Provides a method to add specific ionising photon luminosity to a grid. (This needs improving to account for necessary unit conversions).
• Provides a method to allow plural and singular axis keys (or just generically alternative naming of axes).

I have implemented it in install_bc03-2016 and install_bpass2.3 as a demo of what it would look like in a simple and complex case.

Issue Type

• Enhancement

Checklist

• [x] I have read the [CONTRIBUTING.md]()
• [x] I have added docstrings to all methods
• [x] I have added sufficient comments to all lines
• [] I have made corresponding changes to the documentation
• [x] My changes generate no pep8 errors
• [] I have added tests that prove my fix is effective or that my feature works
• [] New and existing unit tests pass locally with my changes