sardana device compatible with zmq server

[lrlunin]

make this device compatible with https://github.com/lrlunin/pytango-moenchZmqServer implementing the multiple output images as axes

[lrlunin]

https://www.sardana-controls.org/devel/howto_controllers/howto_motorcontroller.html#multiple-motion-synchronization

[lrlunin]

• [x] missing trigger signals fix
• [x] prepareOne save locally and then assign in prepareAll. otherwise the element on axis 0 need to be in the measurement group...