Refactor database structure for better sync

[divadsn]

Models should work for both systems.

[divadsn]

We might want to store only the data we need for the UI, such as first and last name, email address or birthday for accounts. The profile picture is stored seperately with own id.

[divadsn]

See #27 for details

[divadsn]

As I decided to not support Karta Krakowska (see #30), I will only re-do the database structure to include less private information. This will also make it easier for me to create the UI.