Add Plugins and improve Thread startup

[MarioszMSFT]

* Adding plugin capability.
  Just add code that implements the IWorkerJob interface to the directory of NetLing.Client
  and it will be loaded during runtime.
  New command line option to select plugin name (-n)

 * Add Thread WarmUp capability
   Each thread performs some time of test, to warmup the server

 * Add P99, P95 reporting from command line

 * Start all thread together testing server
   If yoo many threads are used, some threads used to start earlier
   Add an event that controls the start of work on all threads

[MarioszMSFT]

Hi,

thanks for sharing this tool with the community.
I have made some improvements, and wonder if you are interested in pulling this in the main branch.

please keep up the great work,

Marios