Don't automatically stage files added to source control

[isc-vgao]

This fixes #303

Testing Steps:

1. In git-source-control repo, checkout noStagingForAdd branch

git checkout noStagingForAdd

2. Load git-source-control into the current namespace

zpm "load <path to local git-source-control repo>"

3. Create a new class.
4. Add the class file to source control.

git add <path to file>

5. In Management Portal Favorites section, open git-source-control UI and click Workspace on the side navigation menu.
6. Verify that the new class you added in step 3 doesn't show up in Working Copy or Staging Area sections.
7. Modify the class you added in step 3 and save.
8. Verify that the class now shows up in the Working Copy section.
9. Click "Stage" button in Working Copy section.
10. Verify that the class now shows up in the Staging Area section and is no longer in Working Copy section.
11. Refresh the page, click Workspace on the side navigation menu and verify that the class still shows up in the Staging Area section.
12. Click "Unstage" button in Staging Area section.
13. Verify that the class now shows up in the Working Copy section and is no longer in Staging Area section.
14. Delete the class you added in step 3, refresh the page, click Workspace on the side navigation menu and verify that the class is no longer in Working Copy or Staging Area sections.

[isc-tleavitt]

Whoa - wasn't expecting this to be fully a UI issue. Good catch!