.inspectHeader: Inspect 'matr' and check if 1st line can be used/converted as header
Description
This function inspects 'matr' and check if 1st line can be used/converted as header.
If colnames of 'matr' are either NULL or 'V1',etc the 1st row will be tested if it contains any of the elements (if not, 1st line won't be used as new colnames)
If 'numericCheck'=TRUE, all columns will be tested if they can be converted to numeric