Integrate bookmark grid view mode with list view mode.

This way the two different modes can share code and have
all the same behaviors (i.e. context menu options).

AndroidManifest.xml
Remove BookmarkGridPage, which is no longer an Activity.

bookmarks.xml
Add a menu option to switch between the different viewing modes.

strings.xml
Name for that menu option.

AddNewBookmark.java
Remove copyTo, which is not necessary.

BookmarkGridPage.java
Change to just be a GridView, with our desired settings, and
overriding onSizeChanged to size the thumbs appropriately.  Now its
constructor takes a BrowserBookmarksAdapter, which it uses instead
of its old private Adapter.

BrowserBookmarksAdapter.java
Now has two modes, so it can be used for both the bookmarks grid
and the list view.  Removed a bunch of obsolete code, which was
used for searching/sorting the bookmarks.

BrowserBookmarksPage.java
Now switches back and forth between using a GridView and a ListView.
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 6ad436e..5f158a2 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -167,6 +167,9 @@
             currently on, but is not visible because the bookmarks page is 
             showing. -->
     <string name="bookmark_page">Bookmark last-viewed page</string>
+    <!-- Menu item in the page that displays all bookmarks.  Switches between
+            a vertical list view and a grid view which shows thumbnails -->
+    <string name="switch_mode">Switch viewing mode</string>
     <!-- Summary text under the New Bookmark item on the Bookmarks screen.
             Tells the user that if they select this item, it will bring up a
             dialog to bookmark the page that the browser is currently viewing,