update uni dtl callback parameters to match audit fixes

[wenfix]

Closes #218

[0xJem]

This looks ok, but I think you need:

• Unit tests on prepareBaseDTLParameters()
• Some validation in prepareBaseDTLParameters() that the basis points values are within range (i.e. throw an error loudly)
• Document the values sent by form fields into prepareBaseDTLParameters()

[edmulraney]

@wenfix - probs a good idea to add some unit tests as Jem suggests, as its handling funds