Remove Database Config From Setup Process

[alpipego]

In general, the included SQLite database should be used in development as it makes it easier for users to see content directly after setup (e.g., if they're not willing/able to set up their own GitHub app).

If a user wants to use their DB, they'll still be able to do it by changing the config file manually.

[alpipego]

@hofmannsven I prefer this over adding the password to the setup process.

[alpipego]

For the password-protected database, please follow-up in #29

[hofmannsven]

I think we can remove the database config from the setup process as the default setup with SQLite works just fine.
Let's keep the setup as simple and short as possible.