Made a start on new cat functionality. Fields can now be concatenated along a new ax. Projects now have a cat method allowing a field to be concatenated across exper objects, where a new axis and coord are created where points correspond to individual expers. Made insert method for projects, allowing params and fields to be inserted: this is useful for the new cat funcionality. Made param2gr method for project: allows exper param to be used to construct new coord, along which fields belonging to each exper are set as slices. exper objects now have a params attribute that is a dictionary of name vs single value.