CU-8692zn14d: Add missing seaborn installs where necessary

[mart-r]

Parts 3.2, 4.3, and 5 used seaborn, but it was not installed nor is it a requirement for medcat.

So added the install where appropriate, alongside adding it to requirements-dev.txt.

Thanks to @mkorvas for pointing out the issue.

PS: It's odd that the smoketests didnt smoke out this issue, though.