Allow reconnection to running script

[bugy]

If user reloaded (or opened and then closed) a page, he should still see and control currently executing script.
At the moment this is possible only within opened page.
Also, #94 config should be removed - all the scripts should have a possibility to run in disconnected mode

[bugy]

Done.
The setting "kill_on_disconnect" was removed. Now it's always true (i.e. closing a web page won't affect execution).
While script is running, it's always possible to connect to it, even from multiple windows/tabs. In this case all of them should recieve identical information regarding output and downloadable files.
If no user session is active and execution finishes, then opening the web page should show script results. However in this case, the results will be shown only on the first page open.

[bugy]

This issue has a large leak with running behind a proxy without authentication. In this case all user IPs are replaced with the IP of the proxy and script-server thinks, that it's the same user all the time.
We can get real user IP via X-forwarded-for header, but it's vulnerable to attacks, so this improvement should be done in a smarter way.

[bugy]

Moved proxy IP issue to a separate task, since it's related not only to active executions: #114