Implement actual monetary input for transaction values (UX)

The current transaction value input requires the user to type the decimal separator. It would be way better to have a proper monetary input that handles that.

For example, the initial value would be 0.00. Then, the following sequence would be followed to enter 58.76:

• User types 5, input value = 0.05

• User types 8, input value = 0.58

• User types 7, input value = 5.87

• User types 6, input value = 58.76