Better output readout for complex mechanisms

[sg-s]

Since everything (and byt that I mean)

1. output readout
2. previous state read out
3. state readout

is handled via mechanism::getState(), and since that is fairly explicit, there is now a possibility of naming the different outputs of each mechanism (useful when output_mode=1)

Some problems:

what happens when a mechanism doesn't return a member, but a computed value?