Automatically push event changes to web client

[podliashanyk]

Need to decide on the implementation first. Several ways to keep events in the web client up-to-date were discussed:

• polling by the client (howitz)
• polling by the library (zinolib)
• push by the library (zinolib)
• server-sent events

[hmpf]

Zinolib shouldn't have to care that a program is webbased or not, so any web-specific method to push is out.