WiP on selectable mosaico templates.
TODO: Make files always point to trusted URL, such that we don't have to rebase them. They are public anyway. The same goes for mosaico endpoints: /mosaico/templates and /mosaico/img
Custom forms list
Updated DB schema (not yet implemented in the server, which means that most of the server is not broken).
- custom forms are independent of a list
- order and visibility of fields is now in custom_fields
- first_name and last_name has been turned to a regular custom field
