find the best match between source and one of the targets.
updates the matched target text component
returns best matching
the algorith, creates possible matches in 4 directions,
and then sorts matches according to grade.
a grade factor is addd if only 1 match is feasible
creates a matching of both source and target, calculating the matching grade
it does not update the source and target about the matching
if target is also an input component, grade is set to NOMATCHGRADE