Add leads 3 support

[koertho]

This PR adds support for leads 3.

Since Leads 3 do not offer the storeLeadsData hook, I needed to use the processFormData hook, where I load the corresponding leads data set. I also needed to adjust some code to make it compatible with haste 5 and changed database field names. The code should be compatible with haste 4+5 and lead 1+3.

[fritzmg]

Me and @aschempp floated a different idea a while back. iirc it might make more sense to store the duplicates serialized into the respective fields. So if you have a field called name in your form which can be duplicated, you won't have name, name_2, name_3etc. - but rather you will havenamewith the valueName 1,Name 2,Name 3`.

@koertho wdyt?

Although I don't know how it should handle checkboxes (not sure how it is handled now).

[koertho]

The current way is better for my case, if I understand correctly, since I store first and last names and keeping them together makes more sense :)

[fritzmg]

Thank you @koertho