Add a DB init to create a specified user for the demo

[kakru]

At the moment the provided db.sqlite file consists only one user, and it's not possible to play with the demo, cause creating new users is not implemented. Please add missing files for the demo or regenerate DB at startup creating the first user according to some easily editable config data.

If one wants to play with the demo, I suggest editing db.sqlite - adding a user to the 'users' table, and than connecting social network accounts (for sqla version of the demo).