Maintenance release und minor bugfixes

[FEATURE] Added signal sendUserMessageCustomAttachmentData #675
[FEATURE] Add possibility to hide certain module actions #637
[BUGFIX] Fixed encoding for text in iCal file #678
[BUGFIX] Fix Exception in ExportService #682
[BUGFIX] Ensure hidden/deleted field is ignored in FieldValue getters #684
[BUGFIX] Make getter/setter for location latitude upperCamelCase #685
[TASK] Add flexform setting for detail page
[TASK] Replace folder icon with a SVG version #681
[TASK] Added "extenstion-key" to composer.json #683
[DOC] Updated documentation about settings.event.errorHandling #676
[DOC] Updated documentation about JSON-LD data #572