implement api level toggling

and rename navtree.js to android-developer-reference.js for all reference related scripts
 TODO: shading for hidden classes in the treeview navigation... these aren't dynamic yet.

tools/droiddoc/templates/classes.cs

@@ -22,7 +22,7 @@
 <table class="jd-sumtable">
     <?cs set:cur_row = #0 ?>
     <?cs each:cl = letter ?>
-        <tr <?cs if:count % #2 ?>class="alt-color"<?cs /if ?> >
+        <tr class="<?cs if:count % #2 ?>alt-color<?cs /if ?> api apilevel-<?cs var:cl.since ?>" >
             <td class="jd-linkcol"><?cs call:type_link(cl.type) ?></td>
             <td class="jd-descrcol" width="100%"><?cs call:short_descr(cl) ?>&nbsp;</td>
         </tr>