presence: Add JSON config class

Add a JSON config class that will be used to parse a given JSON config
file and generate the fan presence policies from that config.

Tested:
    N/A

Change-Id: Iac1703ea8d9e1e1d0d40e15a58145181d4f1a0f9
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
4 files changed