Make packaging/installing in /usr easier

PR does 3 things really:
1- make everything a bit more unix'y - agent goes in /usr/bin/ conf is expecting to be in /etc (old style is supported), static files go in /usr/share (certs), libs only go in /usr/lib/node_modules/ (nearly...) and setup does a 'global' install. You should still be able to run the agent by running /bin/agent.js
2 - systemd support (allows systemd people to not depend on forever) - sysV script still needs work
3 - sensors-list now expects to be in someone's home dir - but the systemd script runs as no-one so either a user needs to be created on setup (iotkit-agent?) or simply change the file to use an existing user.

Hopefully this is an easy sell :) The only downside is the lack of non global install in the setup script, I could add that but since sudo/root was enforced before I'm not sure anyone was seriously using it? It still works if you remove the -g.

Since I'm changing all the paths it'd be good to get someone to have a second look - it worked for me on Arch Linux but I havent done much testing bar registration worked and the journal was clean.