Adds "Now" page functionality

Implements a "Now" page to share current activities, inspired by nownownow.com.

- Introduces a new content type "now" with corresponding layouts and archetype.
- Adds a "Now" entry to the main menu.
- Creates a script to easily generate new "now" entries.
- Updates the colophon page with information about the "now" page.
- Deletes weeknote config as it isn't in use anymore

config/_default/menu.yaml

@@ -19,6 +19,10 @@ main:
     name: "Series"
     url: "/series"
     weight: 27
+  - pageRef: "/now"
+    name: "Now"
+    url: "/now"
+    weight: 28
   - pageRef: "/explore"
     name: "Explore"
     url: "/explore"