Allow to override acquisition parameters during qspace conversion

This MR adds the possibility to override acquisition parameters (beam energy, direct beam center and channels per degree) for each qspace conversion. By default, values provided during merge are used. This information is now saved in qspace hdf5 files and displayed in 'info' group of the qspace in the tree view.

This is compatible with older qspace file, and new files can be opened with older xsocs.

closes #11 (closed)