Fix compile for MSVC2013

[mjmckp]

Fix compile for MSVC2013 by explicitly implementing move constructor and operator which previously caused the compile error:

3>d:\upscaledb-fork\src\2device\device_disk.h(61): error C2610: 'upscaledb::DiskDevice::State::State(upscaledb::DiskDevice::State &&)' : is not a special member function which can be defaulted 3>d:\upscaledb-fork\src\2device\device_disk.h(62): error C2610: 'upscaledb::DiskDevice::State &upscaledb::DiskDevice::State::operator =(upscaledb::DiskDevice::State &&)' : is not a special member function which can be defaulted

[cruppstahl]

Thanks!