Add UI for switching and managing terminal sessions.

Add UI for switching and managing terminal sessions.

We expose three different ways to manage terminal sessions:

* Options menu items to open a new window and close the current window.
* A WindowList activity, reachable from the options menu, which lists
  all the open windows and allows opening, closing, and switching of
  windows.  The behavior is patterned after the window list activity in
  the Android browser.
* Gestures to change windows -- swipe right-to-left for the next window,
  left-to-right for the previous window.

The options menu items have been reordered to make what should be the
five most frequently used items (new window, close window, window list,
toggle keyboard, special keys reference) appear in the icon menu so that
the user doesn't have to touch "More" to reach them.

This patch adds several icons.  btn_close_window and ic_menu_windows
come from the Android browser source, while the rest come from the
Android 2.3.3 SDK platform, revision 2 (platforms/android-10/data/res).