Only in such mode multithreading is allowed. 
In async mode one can meaningfully use send completion callback.
Default mode is synchronous (as before), which allows to use handler
only from main thread

Now no queues are allowed, all operation are confirmed by WS handler

Now one can directly register WS handlers to THttpServer
If allowed, handlers can be precessed directly in the civetweb threads
without involving of THttpServer thread at all. 
This allows to run many connections for many different web widgets
absolutely independent from each other - there are no one bottleneck in
http thread (or any other main thread)

web socket engine should support this (default off) and
web socket handler have to allow this

In case of long poll engine requests should be holded until next send
operation from the server starts. To correctly resolve ownership,
shared_ptr should be used on all stages of processing

One could send now binary messages viw websockets, 
which result as Blob objects on JavaScript side. 
Also combined send of string header and raw buffer will be supported.
For special engines (like longpoll) this will be handled in single
request.

remove inheritance from TNamed, 
change signature of PreviewData() and PostProcess() methods

Now all WS connections and correspondent THttpWSEngine instances
preserved in the THttpWSHandler. User only works with WS Id (UInt_t) and
use it to accept connection, close connections, send data via connection