During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
This converts the media servlet URLs in the same way as
(most) of the rest of Synapse. This will give more flexibility
in the versions each endpoint exists under.
* Removes the `v1` directory from `test.rest.media.v1`.
* Moves the non-REST code from `synapse.rest.media.v1` to `synapse.media`.
* Flatten the `v1` directory from `synapse.rest.media`, but leave compatiblity
with 3rd party media repositories and spam checkers.
