Continuing UI for new SDK Manager Packages Page.

Continuing UI for new SDK Manager Packages Page.

- Changed application to not display the "page selector" anymore.
  Instead there's only one page, which is is the available+installed
  packages combined page.

- The app behavior depends on the env var.
  - When set, it becomes the "SDK Manager" to only deal with packages.
  - When unset, it has the previous look & pages to deal with both
    AVD and SDK packages.
  - Eventually we'll also have an AVD separate app and we can
    factor out/cleanup the old window implementation.

- Integrated the progress bar + status in the page.
  - This isn't linked to Eclipse yet.
  - The ProgressTask* classes deal with the old behavior of
    a separate progress dialog.
  - The new ProgresView* classes deal with the new behavior
    of the progress status incorporated in the main page.

Other changes:
- Changed layout of the new package page
- Center add-on sites dialog on top of parent.
- Display "details" in tree view (e.g. includes obsolete
  packages + all archives)
- Plug in logic for install/delete buttons

Change-Id: I84c021cb7104681bb39445bd79ab01e161a22796