Make packaging and global installing of agent easier

* moved agent.js to bin/ dir
* made all path names more unix-like to provide a 'clean' systemwide install
* made forever optional in setup-agent.sh
* setup-agent.sh now works globally

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

Using systemd(1) we can replace forever and use the init process to restart the
application. The setup script should install it on machines using systemd.

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
.npmignore: add ignore file to make packaging cleaner

This enables a clean /usr/lib/node_modules on install

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