Add an item next to status bar to show which PR we're on

[jcansdale]

Add control here so @donokuda can start experimenting with UI

[jcansdale]

It looks like there's a SccStatusBar where Visual Studio's Git related UI lives. I'll see if I can put something into or next to this.

There's a Microsoft.TeamFoundation.Git.Controls.SccStatusbarService in Microsoft.TeamFoundation.Git.Controls.dll. I'm guessing this is related.

Here's a dump of ITeamExplorerSection from Visual Studio 2015:
https://gist.github.com/jcansdale/ccbd48644efbcbd6b3fb7242dc759dea

The pertinent section is:

Microsoft.TeamFoundation.Git.Provider.Status.StatusSectionVS (Microsoft.TeamFoundation.Git.Provider.dll)
   ParentPageId: B38F4ABC-2B2C-4E4D-A047-EAACA7514610
   ExportTypeIdentity: Microsoft.TeamFoundation.Controls.ITeamExplorerSection
   Id: 7C7C4B42-7E76-44A0-B5EC-C8D35A9572DB
   PlacementParentPageId: 1B6304DB-275E-47CC-A026-2F443723EC15;D0E4EA4E-24F0-46D6-9D07-0BC09CDEAE7D
   PlacementPriority: System.Int32[]
   Priority: 5
   ContractType: Microsoft.TeamFoundation.Controls.ITeamExplorerSection
   ContractName:

Here's a tree of controls in Visual Studio 2015:
https://gist.github.com/jcansdale/3aec16975471f1ee7e9a35a334b33e11

SccStatusBar is added to MainWindow (both are in the Microsoft.VisualStudio.PlatformUI namespace of Microsoft.VisualStudio.Shell.UI.Internal.dll).

The SccStatusBar seems to be very much a special case, which is the only element to have a TemplatePart attribute defined on MainWindow.

namespace Microsoft.VisualStudio.PlatformUI
{
	[TemplatePart(Name = "PART_SccStatusBarHost", Type = typeof(Border))]
	public class MainWindow : CustomChromeWindow, IComponentConnector

Named FrameworkElement components in Visual Studio 2015 (and their types)
https://gist.github.com/jcansdale/32c233f5bcf64968bf6adf7a32890ae0

[meaghanlewis]

Added in #1102