Load GISAS data from three columns csv-table (#580)

Allows import and export of 2D data as 3-column table.

On loading we check axes alignment (only Qy or Qz should change from line to line, not both).

Points (pixels) are assumed to be equidistant, but now we do not check it.

To the moment, q coordinates are not applied to data axes, because the mechanism for setting units is not established yet.

So the data is understood as table of bins.

Resolves #580 (closed)