Add /tasks/all route to website

[kostiak]

Added a route for all tasks in /tasks/all in preperation for adding /tasks/random.

Did not add a link to the page anywhere.

Note: We will need to later decide how to handle the page. Should we add it to a feature flag? Give access to "advanced users" or something?

In any case, this will be useful for dev once we move over to the random tasks.