Unify the repository list / URL tabs of Open from GitHub dialog

[jcansdale]

Summary

Users seem to rarely change the tab they're presented with on the open/clone dialog. This is despite that different tabs would be appropriate when cloning different repositories.

If the user is cloning a recently contributed to repository the repository list would make most sense. If they're cloning a public repository they don't own, the URL tab would be the only option.

By allowing users to enter a URL into the repository list search box, they won't need to change tabs in order to clone/open any repository.

Implementation Ideas

• Add repository in search box to list of repositories
• Add repository in copy/paste buffer to list of repositories
• Allow user to search repositories by exact match URL