MetaArray: make it possible to append multiple axis values
MetaArray: make it possible to append multiple axis values

Example use case: taking an image stack where each frame has a time value AND a position. Previously we could only append new time values.
meganbkratz/acq4,meganbkratz/acq4,pbmanis/acq4,acq4/acq4,pbmanis/acq4,meganbkratz/acq4,campagnola/acq4,acq4/acq4,pmaunz/pyqtgraph,acq4/acq4,campagnola/acq4,pbmanis/acq4,pbmanis/acq4,campagnola/acq4,pmaunz/pyqtgraph,acq4/acq4,campagnola/acq4,meganbkratz/acq4