supprot global element map in nek reader

[yslan]

Checkpoint file stores the global elements id and the reader should remap the data correspondingly.

NekToolKit/matlab/afld_reader.m

Lines 76 to 78 in 2917cc6

	for i = 1:nskip
	fgetl(file);
	end

See KTH's reader as reference:
https://github.com/eX-Mech/nekmatlab/blob/aeffe1be21f9b2c34a189c06ac48fad8fef38b98/readnek.m#L143