As discussed today in the meeting with Marc & Martin (GFZ),
here are some changes:

* No owner field anymore (use contacts only)
* Export control panel is now readonly, as there should
  be a dedicated view in the future.

Updated node images

Closes #78

See merge request sensor-system-management/frontend!102

Same behaviour after save for included elements

Closes #77

See merge request sensor-system-management/frontend!99

Don't show add button if the user is not logged in

Closes #76

See merge request sensor-system-management/frontend!98

Now device api & platform api both follow the same
pattern regarding to the return value of their save methods.

Restructure frontend

See merge request sensor-system-management/frontend!82

Migration to new frontend structure for contacts

See merge request sensor-system-management/frontend!97

Feature restructure frontend platforms

See merge request sensor-system-management/frontend!92

Merge branch 'feature-restructure-frontend-platforms-urn-builder' into 'feature-restructure-frontend-platforms'

Helpers for building URNs

See merge request sensor-system-management/frontend!96

Make include related object optional

See merge request sensor-system-management/frontend!94

Merge branch 'feature-restructure-frontend-page-mixins' into 'feature-restructure-frontend-platforms'

Mixin for attachments

See merge request sensor-system-management/frontend!95