Add more field types to IO_demo

[EdHone]

PR Summary

Sci/Tech Reviewer:
Code Reviewer:

This PR changes the driver of the IO_demo app to use more than one type of field. Before this change, only fields on the WTheta function space are used by the app, but this app expands the field depository to add fields on the W0, W2 and W3 function spaces. The application's main algorithm has been expanded so that the WTheta diffusion is sampled on all the different function spaces. The XML configuration for I/O has also been updated to reflect these changes
These fields have been added to the checksum algorithm at the end of the run, so KGOs have been updated.

Closes #299

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
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Testing

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trac.log

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Performance Impact

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Documentation

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Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

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