Add ability to input a 'custom' value, in addition the form-specified values

[PaulUithol]

Proposal: add the ability to input a 'custom' value for a key, in addition to the set of predefined values in the form

Example: for a bank's operator key, a number of possible values have been predefined (to minimize errors/typos, and cut down on data entry time), like Barclays Bank, Stanbic Bank, Bank of Africa, and Finance Trust Bank. However, these cover only the ones that occur regularly; mappers can encounter other banks, and would need to be able to enter the actual value for the operator for those. So when a mapper find a Tropical Bank (yes, it does exist :), he'll need to be able to type this name instead of choosing one of the predefined values.

[hallahan]

This is currently being tracked as #58