agent.js: move agent.js to bin/ dir

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
agent.js: make agent executable node script

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
iotkit-agent.service: add systemd service file

Using systemd(1) we can replace forever and use the init process to restart the
agent.

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
.npmignore: add file to allow clean install in /usr/lib/node_modules

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
index.js: use global config file if local one not found

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>