Feature: Refresh captcha by click.
Notifications for ws events.
Subscribe to a thread after reconnect. Remove subscribers on exit.
Get captcha once
Fix: captcha for authorized users is enabled.

What steps will reproduce the problem?
- Logout, if logged in.
- Create a post or a thread.
- Login
- Create a post or a thread.
What is the expected result?
- A post or a thread must be created.
 What happens instead?
 - Error message: Wrong captcha
Fix: markdown blockquote not works.
Feature: Enable github flavored markdown extensions.
Disable `header` and `hr` extensions
Small updates in skins.