add Lmod/5.5.3 and adjust nearby files accordingly

Signed-off-by: Fotis Georgatos <fotis.georgatos@uni.lu>
upgrade to 5.6

Signed-off-by: Fotis Georgatos <fotis.georgatos@uni.lu>
Merge pull request #878 from fgeorgatos/contrib_Lmod-5.5.3

add Lmod/5.6 and adjust nearby files accordingly