[Echo.StreamServer.API] switch to polling after configurable timeout; introduce parameter which indicates the reason why connection was closed
[Echo.StreamServer.API] move a fallback config parameters to the websockets; add comments; update close reasons strings;
[Echo.Utils -> random] update docs; update tests with negative numbers cases
[Echo.StreamServer.API] update closeReason states
Merge branch 'neurostep/f1856-polling_fallback_delay' into rc3.0.15