Reducing funding amount

[KarimChabrak]

When project is rewarding through non-issued COIN, reducing funding amount creates an error. Here, user should be able to reduce amount down to the amount of collected COINS.

When project reduces funding amount below the amount received, user gets error. Normally, he should get a message "As you did receive investment, you can not reduce funding target below the amount that you have collected. If you want to give back investment, please cancel your campaign."