Enable Git Extras by Default

Created by: brentshermana

A common feature among text editor extensions with Git integration is the ability to display the last commit message that changed a particular line.

Currently, when viewing a source file on github with SourceTree's browser extension, you can navigate using references to and definitions of symbols. It would also be cool to be able to navigate to the last commit that changed the line you're clicking on (if you're clicking on whitespace rather than code)?