Extend unmount functionality to be recursive

Currently we have the un-mount modus in the configurations platforms-and-devices tab. There we can unmount several devices relatively fast.

What is missing is the option to un-mount on the tree recursively, so that we just select the top level platforms - or even the configuration itself - and do this unmount for every element below.

It will help the users in handling the end of a configuration (after the measuring campaign for example) and to make the devices free to be used somewhere else.