Extend node style functionality

[dan-knight]

Description

Closes #75, #74, #77, #78, and #79. Also includes the below tree as a new end-to-end test case, which tests all new features in this PR.

Example

tree.input <- data.frame(
    parent = c(NA, 1, 2, 2),
    node.col = c(NA, 'grey75', 'red', 'grey75'),
    border.width = c(1, 1, 2, 2),
    border.type = c(1, 1:3),
    border.col = c(NA, 'black', 'black', 'blue')
    );

tree <- SRCGrob(tree.input);
grid.draw(tree);

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]

With the benefit of hindsight after doing more development on the edge style, I opted to remove the node.col parameter entirely. This will be consistent with other style settings, and doesn't change the user's workflow in any meaningful way.