dict generator interface for SSE

[tholzheim]

Based on the progress example it would be nice to have a standardized interface where the contract is:

• A callback supplies dict results in a loop as a generator
• The SSE blueprint automatically sends the corresponding JSON to the client
• On the client side the javascript code unpacks the json
• In principle now a name/value message stream between server and client has now been established

[tholzheim]

Example:

• progress bar example from fb4_examples
• search bar suggestions ?
• Table completion on the fly while calculating

[WolfgangFahl]

Looks good to me. What needs to be done to close this issue?