feat: pass context to page extensions

Pass the context to page extensions to allow them to make decisions
based on the context. For example, an extension to load the course
specific scripts. This is currently not possible because the course
details are not availale to the page extensions. Made this possible by
passing the context to page extensions.

school/plugins.py

@@ -24,6 +24,11 @@ class PageExtension:
     `render_footer()` methods to inject whatever styles/scripts into
     the webpage.
     """
+    def __init__(self):
+        self.context = frappe._dict()
+
+    def set_context(self, context):
+        self.context = context
 
     def render_header(self):
         """Returns the HTML snippet to be included in the head section