Support timing and profiling

[mperdeck]

Add capability to loggers to start and end a timing block.
The loggers at each end of the block will have the same name (creating the association between the two).
In console appender, they create a group, to make it easy to see the timing block.

In console appender, where possible they do profiling (console.profiling, avail on firebug)

Opion to always send the time elapsed, or to only send message on timeout (took too long).

Something like
JL().info().startTimer()
...
JL().info("time taken by ... is").sendElapsedTime()

or

JL().info().startTimer()
...
JL().error("time taken by ... is too long:").sendTimeOut(timeOutInMs: int)