Fix globals in heatmap functions

[dan-knight]

Description

These changes fix the Undefined global functions or variables R CMD check NOTE, as well as inevitable runtime errors. Some of these helper functions should be refactored or reimplemented, but this is beyond the scope of these fixes.

Checklist

• [x] This PR does NOT contain PHI or germline genetic data. A repo may need to be deleted if such data is uploaded. Disclosing PHI is a major problem.
• [x] This PR does NOT contain molecular files, compressed files, output files such as images (e.g. .png, .jpeg), .pdf, .RData, .xlsx, .doc, .ppt, or other non-plain-text files. To automatically exclude such files using a .gitignore file, see here for example.
• [x] I have read the code review guidelines and the code review best practice on GitHub check-list.
• [x] I have set up or verified the main branch protection rule following the github standards before opening this pull request.
• [x] The name of the branch is meaningful and well formatted following the standards, using [AD_username (or 5 letters of AD if AD is too long)]-[brief_description_of_branch].
• [x] I have added the major changes included in this pull request to the CHANGELOG.md under the next release version or unreleased, and updated the date.

[dan-knight]

everything looks good, seems like the get.colours and data.frame.to.matrix are still the original? either way it looks like it would do what it needs to

Just renamed and maybe slightly simplified. No real changes from yours. I didn't want to include any real functional changes here, just enough to fix the problems in R CMD check.