Highlight files in stack frames

[jakobjpeters]

Often, the important stack frames come from local files or the REPL. This highlights those files so that they are easier to identify visually. This should make it easier to debug errors by drawing the developer's eyes to stack frames from code that they "own".

The implementation is careful to match the file color with the cyclic module color. I'm not yet sure how to implement this for the top-level scope REPL case.