The categories.html template is used in three places:
1) for the tabs on the result page
2) for the default category selection in the preferences
3) for the advanced search category selection in the oscar theme
The search_on_category_select plugin only makes the checkboxes in 1)
behave like tabs. The previous commit however hides the checkboxes
in all three places when the plugin is loaded, which we don't want:
The categories in 2) and 3) always act like checkboxes, so the
checkboxes in these places should actually always be visible.
This makes it easier to separately handle search and index requests
from a web server or from a reverse proxy.
If a request to index contains a query, a permanent redirect HTTP response
is returned. This should give some level of backwards compatibility
for users that have set a searx instance in their browser's search bar.
