Document Show PDF support

[edulix]

Since we are ending up merging the PRs in https://github.com/sequentech/roadmap-internal/issues/1 we will document this feature in the documentation repository.

Master PRs

• Support showing PDF in start-screen iam#240
• Support showing PDF in start-screen voting-booth#269
• Support showing PDF in start-screen  common-ui#249
• Support showing PDF in start-screen ballot-box#134
• Documenting show_pdf feature flag #91

Master bugfix PR

• bugfix: show pdf not working as expected iam#243
• bugfix: show pdf not working as expected iam#244

[edulix]

It seems there's a bug: the show_pdf should be in auth_method_config['config'] and not in a auth_method_config. I'll do a bug fix with PRs.

[edulix]

Okey I fixed the last bug. However, I cannot make login work when using email authentication and activating show-pdf. The login page simply simply redirects to the homepage. @Findeton can you review/fix issue this please?

[Findeton]

@edulix The fix was unfinished, I opened a new PR with the rest.