Hide reports list behind a feature flag

[StefanFl]

The reports list is only used to make pdf reports accessible. Now the PDF reports are not supported anymore for more than a year now. This PR hides the list behind a feature flag and renames the button in the report builder to just "Run". Goal is to avoid misunderstandings of users.

Additionally it removes the upper button to generate a report in the report builder because it is redundant and looks different than the one at the bottom.

Shall we additionally include a message, that PDF reports are deprecated and removed in the future, eg. 30.6.2021?

[valentijnscholten]

I see that this feature also kinda re-enables the pdf reports. Are they working correctly? It could still be an interesteing fearure if the PDFs look nice. But it's just wikihtmltopdf I think, so they might be not so nice looking. Similar to "print to pdf" from the browser they look pretty poor, no colours, etc.

[StefanFl]

I tried to test wkhtmltopdf with docker, but it is problematic because the library needs an X11 server. So it's only usable in a source installation what we don't support anymore. If you can't produce a PDF export like it is now, then the reports list dialogue could be disabled completely right now as well. The feature flag with the PDF as a choice is a consistent way to leave the current functionality available for people who need it.

Marking the current way of producing PDF as deprecated and remove it from the source 3 months later would be what I propose. If someone needs PDF reports, then it might be the best way to start from scratch with a Python based library.

[valentijnscholten]

Yes, so we merge this but also create a github issue labeled with "2.0.0" for removing PDF reports alltogether. I think there's a lot more code around that, also in the API to generate reports etc.

[StefanFl]

Yes there is some more code that are obsolete. I can write the issue for removing the PDF reports later today.

And I would like to make a note in the documentation about removing the PDF reports. Can do it in a second PR later this week.

[Maffooch]

Good fix for now to reduce the questions.
+1 for removing altogether in a 2.0 of sorts

[StefanFl]

The issue to remove the code for PDF reports is #4077. Please attach it to milestone 2.0 as discussed. Thank you