Switch CTRL and SHIFT when multi-select labels

[haesleinhuepf]

Hi @frauzufall ,

while testing the selection of labels in the label editor, I realised that the behaviour of SHIFT and CTRL should be switched. I'm not sure how it is on Linux, but at least MacOS and Windows users are used to hold CTRL to select multiple objects, e.g. in Finder/Explorer.

Thanks!

Cheers,
Robert