Implement #231 – default slot filling (#269)

* Add 'default' slot option + implicit fills; tests; docs
* Differentiate between standard fillnodes and implicitfillnodes on type lvl
* Reworking slot-fill rendering logic. Simplifying component interfact. Add new get_string_template method
* First working implementation of chainmap instead of stacks for slot resolution
* Stop passing FillNode to Component initalizer -> better decoupling
* Treat fill name and alias and component name as filterexpression, dropping namedvariable
* Name arg of if_filled tags and slots must be string literal

django_components/component_registry.py

@@ -34,3 +34,24 @@ class ComponentRegistry(object):
 
     def clear(self):
         self._registry = {}
+
+
+# This variable represents the global component registry
+registry = ComponentRegistry()
+
+
+def register(name):
+    """Class decorator to register a component.
+
+    Usage:
+
+    @register("my_component")
+    class MyComponent(component.Component):
+        ...
+    """
+
+    def decorator(component):
+        registry.register(name=name, component=component)
+        return component
+
+    return decorator