SSE plugin Refactored
Refactored Client class

Now each application have separated Client class: application.Client
(with different prototypes), previously was one class impress.Client for
all applications
Refactored WebSocker plugin
Fixes in SSE plugin and examples
Events plugin separated from SSE plugin
Merge pull request #71 from tshemsedinov/plugins

Cumulated stable updates from "plugins" branch