Kill query request

[anselvo]

We need to kill query request to postgres if frontend doesn't wait for response anymore.

• graphs request (probably it would be nice to add timeouts as well, it can consume a lot of RAM if db has a lot of tables)
• query builder request (it can be useful only for console, because for template query we have logs)

It is not possible to kill reuqests via http protocol, we either need to consider:

• make this requests async to get pid and cancel them
• use some websockets to be able to close connection and detect it