Removes a large number of image assets that are no longer used by the site. This reduces the size of the repository and the deployed site.

These images include various sizes of favicons, touch icons, cover images for old blog posts and weeknotes, and character images.

The `make-post.py` script is adjusted to correctly format the year in post paths.

- Introduced a custom DateInput widget for Django forms to set the input type to "date".
- Added a simple template tag `url_replace` to modify GET parameters in URLs, facilitating cleaner navigation between views while preserving search filters.
- Documented the usage of both features in a new post for better understanding and implementation.