Create abstract gallery display

[MaHaWo]

• add a general GalleryDisplay component:

  • have a gallery containing arbitrary components as its tiles
  • use this for frontpage and childrenoverview
  • searchable

• add dummy childrenoverview page

• make CardDisplay more flexible wrt styles

• adjust bottom navbar to be able to switch next/previous buttons on and off

  • makes it usable if only a help or info button is needed

• minor corrections of variable names and stylings.

• not included:

  • paginated children overview
  • indicator functionality if survey for a child is incomplete (on account of lack of backend)

[MaHaWo]

@lkeegan I changed the style of the image and removed the background from the dummy images. Do you want to have another look?

[lkeegan]

lgtm!