Add support for image component in PDF-generator

[lorang92]

Description

In Altinn/altinn-studio#379 we added support for an image component. We should also support this in our pdf-generator.

Acceptance criteria

• PDF generator handles images

Specification tasks

• [ ] Respect alignment?
• [ ] Display image possible? What do we support? Any limitations?

Development tasks

• [ ] Add support for image component

Test

Add test cases here as checkboxes that are being tested as part of the changes.

Definition of done

Verify that this issue meets DoD (Only for project members) before closing.

• [ ] Documentation is updated (if relevant)
  • [ ] Technical documentation (docs.altinn.studio)
  • [ ] User documentation (altinn.github.io/docs)
• [ ] QA
• [ ] Manual test is complete (if relevant)
• [ ] Automated test is implemented (if relevant)
• [ ] All tasks in this userstory are closed (i.e. remaining tasks are moved to other user stories or marked obsolete)

[SandGrainOne]

All PDF content related features are now outside the scope of the PDF-generator. The PDF-generator will be built to generate PDF from HTML produced by the Apps.