UR: proof states are not updated after proving new conjectures!

[yutakang]

In the current implementation, proof states are not updated after proving new conjectures!

Therefore, subsequent proof attempts are unable to take advantage of such proved conjectures.

This needs to be fixed.

[yutakang]

Probably I can do something similar to what I did in Australia for Cogent.

[yutakang]

That is, use Local_Theory.note (a, ths).

[yutakang]

I have to use Proof.theorem to update Proof.state using Local_Theory.note as is done in this code.