[DOC] BACKLOG-1314 - Document the REST calls for Carte (Kettle Path) Part2

What was done:
1) added JMeter tests for the servlets required
2) added comments to the classes
[PDI-12947] one connection pool created per step
[PDI-13049] - Regression: PDI 5.1 Clone Rows NULLs
Merge pull request #856 from SergeyTravin/PDI-12947

[PDI-12947] one connection pool created per step
Merge pull request #861 from akhayrutdinov/PDI-13049

[PDI-13049] - Regression: PDI 5.1 Clone Rows NULLs
Merge pull request #859 from kolinus/BACKLOG-1314

[DOC] BACKLOG-1314 - Document the REST calls for Carte (Kettle Path) Par...
[BACKLOG-1479]: Implement support for Carte parameters (threads and connections)

Implement necessary code changes to support configuring the following options for Carte:
acceptors, acceptQueueSize, lowResourcesMaxIdleTime.
lowResourcesConnections option is not supported by org.mortbay.jetty.bio.SocketConnector that is used in the current implementation of Carte web server so it's out of scope.
Also there are unit tests.