Show gross amount of Contribution when User choosed to pay fees

With this branch merged, we will always use the amount paid by user as contribution's amount.

# With existing implementation
```
Contribution #1
- value                = $100
- payment service fees = $9
- fees paid by user?   = yes

Value of the contribution, like when emailing the user or on tweet button: $100
```

# Accepting this change
```
Contribution #1
- value                = $100
- payment service fees = $9
- fees paid by user?   = yes

Value of the contribution, like when emailing the user or on tweet button: $109
```

/cc @neighborly