Resolve "Memory consumption of latest changes in TQMultiObservable"

Release notes

Temporarily disabled lazy evaluation of TQMultiObservable's subObservables due to large memory consumption, i.e. now statements like a ? b : c will evaluate both b and c. The old behaviour can still be activated by setting evaluateSubObservablesLazily is set in the master configuration.

Details

This will need to be followed up to still provide the additional flexibility but without increasing the memory usage as much as this currently does (see issue for example). The tag evaluateSubObservablesLazily can be set in the master configuration to enable the lazy evaluation again.

Closes #220 (closed)