Keep formatting of commit message

**How it currently works**
A commit message will be squashed (all whitespace removed, including linebreaks) in commit list and commit diff view.\
The original formatting can still be seen in commit overview.

For the commit list, this is fine, but in the commit diff there is enough space and one might want to read the message while reviewing the changes.

**How to improve**
Show the original commit message in commit diff view without stripping whitespace and (more importantly) linebreaks