Adds a list view showing the list of repositories
that VS knows about and that are associated with
the github connection (i.e., the remote url corresponds
to the github connection section information)

Conflicts:
	src/GitHub.Exports/Primitives/UriString.cs
	src/GitHub.Exports/Services/Services.cs
	src/GitHub.VisualStudio/Base/TeamExplorerItemBase.cs

The repository list is loaded from the registry into ConnectionManager.
Don't save it in the cache for now, so it doesn't break compatibility
with the existing cache files and we don't really need to cache it right
now. Let's see how it works just loading directly from the registry for
now.

Offering to open a solution or project is the only way to switch the
context to the new repo. Since it's likely that that's what the user
wants to do anyway (why clone a repo otherwise), let's do that.

The previous logic wouldn't work if there is no active repo in VS

Also fix some issues with refreshing the repo list multiple times and
tracking when local repository list for changes

Make only the repo name bold when active. Change the repo path color to
white when hovering or selecting so it's more visible. Set the
background to selected when selecting with the mouse (different from
just hovering).

Keep the path color white/black when it's the current repo, it's easier
to see.

Fixes #54