F zero dollar connection

Done:
- introduce zero dollar money connections
- make a first visual difference between zero and normal money connections (opacity)
- workable with the 2 money modes
- fixes issue #125 

Needs to be done:
- make a visual difference between disbursed and pledged money coins 
@mrflix I'm not sure how to change the colour of the coins
- afterwards differ visually between disbursed and pledged zero connection