Include ddcks from within ddcks

[zuckerruebe]

As a user I'd like to be able to include ddcks from within ddcks so that I can compose systems in terms of subsystems - recursively.

I'd suggest re-using the include-as syntax which is currently supported in the config files in ddcks like so (e.g. in a ddck representing a building including a heat pump HP)

INCLUDE ...\path\to\heat_pump AS Hp

If the ddck for the house is included as "Build" then a variable :PCond in the heat_pump.ddck file would be expanded to "BuildHpPCond".

An open question would be how to replace nested ddcks with changeDdckFile - if at all.

E.g. the changeDdckFile could be qualified with the "full name" of the sub-ddck:

changeDdckFile BuildHp ...\new\path\to\ddck_file