Parse multiple JSON-format configuration files

- convert from using a single monolithic config file to reading multiple
  files from the directory /etc/pmlog.d
- switch config file format from "ini" to "json"

[GF-3771] pmloglib: Parse multiple configuration files

Change-Id: I3255a7bfd12153082001c0a5e9a518bc5b152020
Open-webOS-DCO-1.0-Signed-off-by: Ameya Palande <ameya.palande@lge.com>
Open-webOS-DCO-1.0-Signed-off-by: Hongjeon Ha <hj.ha@lge.com>