o3tl: cow_wrapper add move constructor/assignment
o3tl: cow_wrapper add move constructor/assignment

Add a move constructor and move assignment operator for
o3tl::cow_wrapper. Insubstantial gains for UnsafeRefCountingPolicy, no
atomic increment needed for ThreadSafeRefCountingPolicy's move-ctor.

Change-Id: Ia2de1ca78b1e0e5a0f30535e752f1dd858fdfef0
Reviewed-on: https://gerrit.libreoffice.org/17848
Reviewed-by: Thorsten Behrens <521e46c8b7e73b40056988e8e9138c484f84490c@CIB.de>
Tested-by: Thorsten Behrens <521e46c8b7e73b40056988e8e9138c484f84490c@CIB.de>

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core