[Enhancement] Adding support for the new "Repositories" button

[blakegearin]

GitHub has added a new "Repositories" button to the navigation bar. This userscript should...

• Add "Repos" text in the "Happy Medium" configuration

• Remove the button in the "Old School" configuration

• For custom configuration...

  • Add the ability to hide the button

  • Add the ability of adding custom button text

  • Add the ability of replacing the button's icon with another

[blakegearin]

First two were added in 1.7.0 (release)