WIP: Rework and add diff view to classification history modal

Description

Closes issues: Related issues:

Start adding diff functionality in classification history modal.

TODO:

• Tested on real classifications. Works about 90% of the time, the diff algorithm sometimes struggle a bit. Will have to tweak a bit more, and then evaluate if it's good and safe enough.
• Doesn't handle when alleleassessments don't have well-formed evaluations (e.g. missing comment fields etc, which can happen for historically imported data). This needs to be improved.
• The red/green background for diff text looks pretty good, but sometimes the users use similar colors which can make it confusing to know whether the text is actually added/removed or just formatted with colors. Should look into even more clear markings.

Notes to reviewer

Type of change

Application (affects UI or general functionality):

• New feature
• Bug fix
• Improvement

Ops / admin / CI related only (not impacting users):

• New feature
• Bug fix
• Improvement

Tests

General

• Tests have been added that prove my fix is effective or that my feature works
• Related tests have been modified/removed

Hypothesis testing:

• Soak testing has been done
• Distribution between positive / negative cases has been checked

Database

• Includes changes to database schema
• Includes necessary database migrations

Configuration

• Includes changes to configuration
• Includes configuration migration instructions in documentation

Merge checklist

• Self-review of code performed
• Feature review against specification (if applicable)
• Need for documentation has been evaluated and, if necessary, updated
• Code and implementation is reviewed by other core developer (all changes, inc. changes based on initial review)