* generate search links for mega collections
** alike old sources list
** configure by setting show_link = true in Amsl.ini

* show descriptions of mega collections
** use collection_description, configure with show_description = true and sub_description_key = 'collection_description'

* configure additional resources manually in Amsl.ini with [AdditionalResources] and entries like:
** mega_collection = source_id

* configure misspelled resources manually in Amls.ini with [MisspelledResources] and entries like:
** wrong collection label = correct collection label for links
** value of "" means no link, only text

* refactore button for collapse / expand all list items in sources-display.js
** disable button while collapsing
** toggle label after collapsing / expanding
** don't expand / collapse already expanded / collapsed panels when clicking

* sort output by source label when configured in Amsl.ini

* refine caching
** encapsulate clearing of cache into own function
** use own namespace
** set default caching time to one day if not configured in Amsl.ini
** cache fully rendered HTML instead of API output
** boosts performance

* remove unused features

co-authored by: Robert Lange <robert.lange@uni-leipzig.de>