Implementation notes: Changes needed if we have products for natural persons

[yolile]

When we have credit products for natural persons we will need to:

• Remove the filters for not inviting natural persons at all
• Restore the filter for showing credit products depending on the borrower's type (see 366 exclude legal person #371)

[jpmckinney]

When restoring the filter 8d0ef0a we should make BorrowerBase use an enum for type. The code in that commit instead compared to a string from the CCE API, which is potentially unstable (and it means Colombia logic bleeds into the model – which it does elsewhere like "COP" defaults, but we try to limit it).