Add support for legacy endpoints

[bassosimone]

@pboothe suggests to use /dash for github.com/neubot/dash and to implement a legacy alias such that /neubot (legacy endpoint) is an alias to /dash (new endpoint).

If we can assume that clients support redirect, then we can implement this using a redirect. It may perhaps be better and more robust to treat the name as an alias on the server side.

(I wonder how we could nudge users to switch to the new endpoint.)

[bassosimone]

After follow-up discussion with @pboothe we agreed that the name should stay neubot and the datatype will be dash because this is reasonable in terms of backwards compatibility.

[pboothe]

To be more specific, the experiment is named "neubot", and it produces the datatype "dash", similar to how we have the experiment "ndt" and it produces the datatypes "ndt5" and "ndt7"

[nkinkade]

This issue seems resolved. Should it be closed?

[pboothe]

This should be closed.