Improve statistics output modstatsdump.f90

[bss116]

This issue addresses code improvement and further functionalities for the statistics routine modstatsdump.f90.
Code improvement: The code has currently some statistics calculations hardcoded for each variable. This should be replaced by generic functions and function calls for the variables. Care needs to be taken about static or dynamic allocation of output arrays, when the number of output variables is only determined at runtime.
Additional features: Adding the block masks as statistics output can be useful for post-processing.
Currently the lowest (floor) level is masked in the statistics output. I would suggest to instead not output it at all and move the z-axes accordingly.

Summary of tasks:

• change to generic statistics functions and calls for output variables

• automate routine for non-neutral and/or scalar statistics output (Automate modstatsdump #42)

• add forcing to output (Assign flow forcing in namoptions #48)

• add block masks to output

• remove masked entries

• only output variables that are actually calculated

[tomgrylls]

As opposed to creating some automated way of changing the size of the netcdf files depending on switches like ltempeq, lmoist etc. A potentially simpler change would be to separate these output files completely. As opposed to having tdump.xxx.nc with all outputs of interest, we have m.tdump.xxx.nc (momentum), T.tdump.xxx.nc (temperature), s1.tdump.xxx.nc (first scalar field) etc. And so on for ytdump, xytdump etc.? This relates to #42.