This change converts the ExtensionManagerView class to TypeScript and

spina.
This also fixes up some issues with our bundles in djblets. The

ExtensionManagerModel was converted to TypeScript, but inadvertently

included in the djblets-extensions bundle instead of the

djblets-extensions-admin bundle. In addition, we had neglected to remove

the other old filenames for the rest of the djblets-extensions bundle

contents from the list.

Ran js-tests.
Used the extensions list in the Review Board admin and saw everything

  work correctly.