multigridFileToSinglegridFiles: Converts a Gridstat multigrid file into temporary single grid files and
returns their path
Description
The format for a multigrid file resembles the single Gridstat data file. The
lines of the single files are simply placed below each other without any
blank lines in between. The function reads in a file and tests if it is a
multigrid file. Multigrid files are seperated into single Gridstat temp
files. The file path for the temp files is returned. If the file is a single
grid files the path is left unaltered.