Remove the requirement for a mesh to be present in the visualisation

[HaivuUK]

Proposed changes

• Fixed the incorrect save units on TOML file and clarified the unit choice on phantom_calibration.md.
• Doc updates to the phantom calibration page.
• Fix to the KaTeX display in web.

Closes #3

Types of changes

What types of changes does your code introduce to LUMA?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of
them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before
merging your code.

• I have read the CONTRIBUTING doc
• I have tested the code locally
• I have added the necessary documentation (if appropriate)

[HaivuUK]

Finish 0.3.3 prep to docs and cargo and tauri versions.
Delete some unused files.
Added version tag to the download button.