Checked out status of PR doesn't update until refresh

[jcansdale]

• GitHub Extension for Visual Studio version: 2.3.7
• Visual Studio version: 2015

What happened (with steps, logs and screenshots, if possible)

1. Open PR detail view from PR list
2. Click on Checkout - branch-name button
3. PR is checked out, but button doesn't update
4. Click refresh button on GitHub pane
5. Button updates to show Local branch up to date

Notes:

• This works fine on current live version (v2.3.6.391).
• This doesn't work on branch fixes/testable-teserviceholder.

@grokys any thoughts?

[grokys]

I think this was caused by #1292. This PR also fixes a bug that we were relying on in TeamExplorerServiceHolder, in that it was previously firing RepoChanged when the status of the repo were changed where it was meant to only be fired when moving to a new repo.

I suspect we'll need to add a StatusChanged signal or similar to TeamExplorerServiceHolder.