improve [un]marshalling of non-binder objects

this change introduces a new class LightFlattenable<> which is
a protocol to flatten simple objects that don't require
binders or file descriptors; the benefit of this protocol is that
it doesn't require the objects to have a virtual table and give us
a consitant way of doing this.

we also introduce an implementation of this protocol for
POD structures, LightFlattenablePod<>.

Parcel has been update to handle this protocol automatically.

Sensor, Rect, Point and Region now use this new protocol.

Change-Id: Icb3ce7fa1d785249eb666f39c2129f2fc143ea4a
diff --git a/libs/gui/ISensorServer.cpp b/libs/gui/ISensorServer.cpp
index 7111092..0b76f37 100644
--- a/libs/gui/ISensorServer.cpp
+++ b/libs/gui/ISensorServer.cpp
@@ -55,7 +55,7 @@
         int32_t n = reply.readInt32();
         v.setCapacity(n);
         while (n--) {
-            reply.read(static_cast<Flattenable&>(s));
+            reply.read(s);
             v.add(s);
         }
         return v;
@@ -84,7 +84,7 @@
             size_t n = v.size();
             reply->writeInt32(n);
             for (size_t i=0 ; i<n ; i++) {
-                reply->write(static_cast<const Flattenable&>(v[i]));
+                reply->write(v[i]);
             }
             return NO_ERROR;
         } break;