Adds new flow component based on type 10 (power law), extended with  a "max flow" value and the possibility to close the connection at the set point "max flow".

This commit to make available, tests will follow.

Compile and run on OS X O.K.
Additonal edit to new afn component.

Compile and run on OS X O.K.
Slight change in new flow component logic, correction of density used. Some documentation added.

Compile on OS X O.K.
Correct code error in last commit, adapt help text.

Compile and run on OS X O.K.
Clarify code comments.

No change to actual code.