Danlooo/use datasets

[danlooo]

Currently, a CellCube uses function Cube to create the array in which all variables are squeezed into just one dimension. Disentangling these variables, i.e. using Dataset instead of YAXArray for a CellCube has the following advantages:

• Allows chunking for separate vars
• Allows loading of vars individually
• Allows individual metadata for each variable