pseq: Create System class

Create a C++ System class that corresponds to the entire system being
controlled by the BMC.

Eventually more function will be added to this class, but for the
initial vers

pseq: Create System class

Create a C++ System class that corresponds to the entire system being
controlled by the BMC.

Eventually more function will be added to this class, but for the
initial version only implement the required support for storing the
chassis objects from the JSON config file.

Create automated test cases for the new class.

Tested:
* Ran automated test cases.

Change-Id: I90b05acb3d17558b4b518c88b45d3d5825165a2a
Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>

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