Enable admins to change the texts in the app

[essoen]

Now developers must change texts in the app manually, but we want the admins to be able to it. This task is basically to implement a small CMS for the app, within the app.

Time estimate: 12 hours

What must be done:

• Add a model, table and endpoints in the API that can hold the texts. The fields in the table should be title, description and text. The name of the table and model should be AdminValues
• Implement a view in the webapp that lists all the elements in texts
• Implement a view that lets the admin edit each text
• Implement fetching the texts from the API and handing these to all components. This can be done by i.e. wrapping all components in one that gives children text data.
• Add the welcome email as a text, and set it to the text described below
• Add the minimumTripDuration as a field in the table
• Add all help texts in the system as texts in the table

Text for welcome email:

Når folk oppretter en profil går det ut en automatisk mail om at profilen er opprettet og at de snart vil høre fra oss. Kan denne infoen bli endret til at noe ala :'Takk for at du har registrert din profil. Du kan nå opprette en reiseforespørsel. Om du lurer på hvor behovet for frivillige er fremover kan du ta en titt på vår nettside eller sende en mail til [email protected]'

This makes #326 obsolete.