Provide a means to edit the text for the campaign pages / Custom settings

[IronRunes]

pages that we should provide support for:

1. Homepage
2. Task completed/get new taks
3. Feedback

[KrzysztofMadejski]

We might allow for custom settings that could be referenced from frontend and managed from admin dashboard.

Acceptance criteria:

• [ ] Interface to define a setting and its type (text, number,.)
• [ ] Editing settings in admin dashboard
• [ ] Easily accessing those settings from views
• [ ] Documentation on above