Only special batch job for creation of images can be started when ROOT
running in batch. Otherwise no any window will be displayed.

One requires temporary profile for firefox.
To create it, one should run firefox -CreateProfile.
When doing this in batch, one also should specify -headless

Only connect/disconnect TGHtmlBrowser signals when it is present

Use assert when detect keys duplication

Clear deistinguish batch and non-batch methods, return bool when
expected

1. use alias for timestamps
2. Define FindOrCreateConnection
3. Remove unused code

One should use ROOT::EnableThreadSafety() call if canvas have to be used
in multithreaded environment

Use recursive, while can be locked many times in different places of
same thread

If same batch job reused second time, one should update drawing
correspondently

When many threads tries to stream same class for first time - it causes
I/O problem while many TClass and TStreamerInfo instances need to be
created. Probably global ROOT mutex has to be used.

If next job will be submitted later - new browser will start

Default is 50 sec.

Use shared_ptr<WebCommand>, keep it inside lambda.
Command also checked if connection gone 

May be required to check if connection was broken or just timed out

Only in such case updates will be delivered to clients - also in batch
mode

To create different images canvas will always start headless browser -
at least now. To generate many files same job will be used.

Batch connection can be used for some dedicated jobs and will be cleaned
up after some predefined time. Normal connections are dedicated for
graphics. It should be allowed to have both of them.

Instead of "start and pray" now WebWindow::Show() returns identifier,
which can be checked for timeout. If application was not started
correctly, one can retry or just simply return with error flag. 

Will be used in all kind of synchronous actions - like image production.

Now URL string contains key which is generated for the new starting
process. It should unique identify connection id. This id can be used in
further operations.

Introduce correspondent constructor signature for contained classes

created

If does not respond after specified time - kill it

Probably, one could create special class for canvas

This items not need to be shared outside connection mutex

Does not work for now, may be later better solution will be found