Add public filters based on meta data (#3673)

* Add public filters based on meta data

* Fix licenseheaders

* ignore empty values

* Fix tests

* Full non-widget implementation

* Widget support

* Add a few tests

* Allow to reorder properties

* Fix isort

* Allow to opt-out for specific events

* Fix name clash between new and old field to make migration feasible

src/pretix/presale/templates/pretixpresale/event/fragment_subevent_calendar.html

@@ -1,6 +1,7 @@
 {% load i18n %}
 {% load eventurl %}
 {% load urlreplace %}
+{% include "pretixpresale/fragment_event_list_filter.html" with request=request %}
 <nav aria-label="{% trans "calendar navigation" %}">
     <ul class="row calendar-nav">
         <li class="col-sm-4 col-xs-2 text-left flip">

src/pretix/presale/templates/pretixpresale/event/fragment_subevent_calendar_week.html

@@ -1,6 +1,7 @@
 {% load i18n %}
 {% load eventurl %}
 {% load urlreplace %}
+{% include "pretixpresale/fragment_event_list_filter.html" with request=request %}
 <nav aria-label="{% trans "calendar navigation" %}">
     <ul class="row calendar-nav">
         <li class="col-sm-4 col-xs-2 text-left flip">

src/pretix/presale/templates/pretixpresale/event/fragment_subevent_list.html

@@ -1,5 +1,6 @@
 {% load i18n %}
 {% load eventurl %}
+{% include "pretixpresale/fragment_event_list_filter.html" with request=request %}
 <ul class="list-unstyled">
 {% for subev in subevent_list.subevent_list %}
     <li class="subevent-row">

src/pretix/presale/templates/pretixpresale/event/index.html

@@ -70,7 +70,7 @@
             {% endif %}
         {% endif %}
 
-        {% if subevent and "date" not in request.GET %}
+        {% if subevent and "date" not in request.GET and "filtered" not in request.GET %}
             <p>
             {% if show_cart %}
                 <button class="subevent-toggle btn btn-primary btn-block btn-lg" aria-expanded="false">