Improved Git Repositories

Public repository page opens in a new window; copy boxes in the design preview

The repository page opens its public page in a new window. The admin design preview tries a tinted surface for click-to-copy boxes.

Changed Open public page on a repository page to open in a new window.

Added to the design preview on /admin/site-look, visible to website admins while the preview is on: click-to-copy boxes (a clone address, an API key, a block of commands) take the section's wash colour mixed towards white, with no border, instead of the theme's translucent white, which is invisible inside a white band.