Add a bunch of instance settings

[danveg]

User story: When running your own instance, you may decide to fix some of the settings for all the groups on your instance. Therefore, some configuration options should be exposed by the Docker images so that they can be set via the coop-cloud recipe.

The instance settings prevail over the group settings:

• If the instance setting is not set, the group setting is available and can be changed for each group. (no change to now)
• If the instance setting is set, the group setting cannot be set and is greyed out.

There might also be instance settings that are not available as group settings.

Complexity: Changes in backend and frontend are needed.

Outcomes (or what needs to be done to move forward): Defining the settings to start with.

[danveg]

Here are some ideas collected from here and there:

Proper instance settings

• Enabling / disabling different Karrot features, such as offers, agreements, and issues
• Allow Karrot instance to make phone number field obligatory
• Enabling / disabling creation of additional groups

Instance settings overriding group settings

• Time zone
• Add setting for weeks activities open in advance to group level

[danveg]

Plus configuring the intervals after which people are marked as inactive and are excluded from the group