SDK Updater: Unzip archives.

This adds the following:
- unzip archives
- if dest dir already exists (typicaly update case),
  unzips in a temp dir then swap dirs then delete
  the old install. In case of error, the old archive
  has not been lost.
- computes stats for download: percentage, speed, time left.
- compute percent for install, on top of progress bar.

The install code will need to move somewhere
out of the window. I think I'll put in the Archive
itself with the window just looping on all archives
and doing some progress bar bookeeping.

tools/sdkmanager/libs/sdklib/src/com/android/sdklib/internal/repository/ITaskMonitor.java

@@ -54,10 +54,16 @@ public interface ITaskMonitor {
      */
     public void incProgress(int delta);
 
+    /**
+     * Returns the current value of the progress bar,
+     * between 0 and up to {@link #setProgressMax(int)} - 1.
+     */
+    public int getProgress();
+
     /**
      * Returns true if the user requested to cancel the operation.
      * It is up to the task thread to pool this and exit as soon
      * as possible.
      */
-    public boolean cancelRequested();
+    public boolean isCancelRequested();
 }