Changed from above/below to auto in association et al.

[TorbjornT]

This pull request changes two things for all \association, \unidirectionalAssociation, \aggregation and \composition:

1. Change the node positions from above/below to auto/auto,swap. This means that the nodes will be placed next to the line regardless of its orientation, and hence solves association: bad alignment of labels for vertical line #12. (I suggested this in https://tex.stackexchange.com/questions/389109/unidirectionalassociation-usage-problem-in-pgf-umlcd)

2. Add the possibility of providing additional settings to the \draw, by means of an optional argument to the macros. Can be useful in cases like https://tex.stackexchange.com/questions/391474/how-to-draw-these-association-using-pgf-umlcd.

[hmenke]

Merged at new upstream: pgf-tikz@5d38f13