(cherry-pick) support installing any .zip file on the sdcard

Replaces the "install sdcard:update zip" menu option with one that
displays a menu of zip files (and subdirs) on the sdcard and lets you
pick which one to install.

Change-Id: Icff541525f2fdfc8939a91af626ecc386ac9dd07
diff --git a/common.h b/common.h
index a767b58..29b37bb 100644
--- a/common.h
+++ b/common.h
@@ -37,7 +37,7 @@
 // Display some header text followed by a menu of items, which appears
 // at the top of the screen (in place of any scrolling ui_print()
 // output, if necessary).
-void ui_start_menu(char** headers, char** items);
+void ui_start_menu(char** headers, char** items, int initial_selection);
 // Set the menu highlight to the given index, and return it (capped to
 // the range [0..numitems).
 int ui_menu_select(int sel);