Graph view: Allow regex filtering across commit message and author

In the Graph/Log view, when the Filter field has regular expressions enabled, the filter should be applied to an internally concatenated string containing the commit's message and author.

This would make it possible to search for commits of a particular topic from a particular developer.

Example commit:

- Message: "Cleanup tracing exceptions"

- Author: "Thomas"

The regular expression  "trac.+thom" should match this commit.