Bug fix in discontinuous member selections for CFSv2

Now it is possible to make discontinuous member selection like in S4, for instance members = c(1,5,7)
New time aggregation behaviour for cumulative variables

time = "DD" performs now sum rather that mean for precipitation (tp) and radiations (rsds and rlds)
Minor change

Empty line deleted
Minor changes
New time format
New behaviour of time aggregation for cumulative variables

Plus some other minor modifications
Modified dictionary for WFDEI
Documentation update
Changes in DESCRIPTION file