Removed usage of QQmlValueType in QQmlValueTypeWrapper

QQmlValueType doesn't have anything really necessary :). Some code it has, but
that was only called from the wrapper, so it was moved there. This also reduces
one level of memory allocation for the wrapper.

In theory the allocation for the JavaScript wrapper could be changed to be the
size of the wrapper _plus_ the size needed for the gadget. However in
anticipation of wanting to be able to move objects, we can't do that as we
can't memmove() gadgets around - they might contain pointers to memory areas
within.

Change-Id: Icb5a6f5513e3b2c87f6639f6f7b1fb572af08137
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix build on MinGW

- alloca() needs malloc.h
- crtdbg.h couldn't be found on MinGW

Change-Id: Ibbf91a58d39ef1e2572baae3c409393acf7aa5df
Reviewed-by: Lars Knoll <lars.knoll@digia.com>