Rename variables used in formulae to clarify inputs and outputs

The components are now c1 and c2 instead of A and B,
in the order of the sequence c1 -> c2 in the data flow.

The output properties (of component c1) are named 'out' followed with the
index, from 1 to N.

The input properties (of component c2) are named 'in' followed with the index,
from 1 to N (when identical) or 1 to M.