SDK Manager: select just new or just updates.

SDK Manager: select just new or just updates.

This splits the "Select New/Updates" link in the
SDK Manager in 2 parts. Behavior is:
- at startup, the sdk manager selects both new and updates.
- one can click on deselect + select new to select
  just new packages.
- one can click on deselect + select updates to select
  just update packages.
- select does not select first, so clicking both new
  then update will produce the previous behavior.

SDK Bug: 20607

Change-Id: Ib861d78b746f4f3c7a8fce421c89ae8094339933