added and index page for series

[frederikhogenbosch98]

added support for an overview page of all series

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[asmecher]

Thanks, @frederikhogenbosch98! Before I review/merge this, could you create an issue describing this change and referring to this pull request over at https://github.com/pkp/pkp-lib/issues/?

[frederikhogenbosch98]

The issue was actually created some time ago, but I believe the pull request was never made.

pkp-lib/issues/6086

[asmecher]

There's another pull request here: #855

Yours seems to be based on that; are you working with that developer, or is this dusting off/updating someone else's work?

[frederikhogenbosch98]

I am indeed working with that developer. Is there a reason why the previous pull request was never merged?