Always use underscores in html ids

Plus some other shifting around

bookwyrm/templates/reading_progress/want.html

@@ -9,6 +9,6 @@ Want to Read "{{ book_title }}"
 
 {% block content %}
 
-{% include "snippets/shelve_button/want_to_read_modal.html" with book=book active=True no_body=True %}
+{% include "snippets/reading_modals/want_to_read_modal.html" with book=book active=True %}
 
 {% endblock %}