35 better require

[rcursaru]

• added NODE_PATH to app.json declaration used by pm2
• changed require to use path relative to project's root, as defined by NODE_PATH
• removed PI_GARDEN_ENV from /etc/environment and added it to app.json declaration used by pm2
• set app.json to be by default in DEV environment; can be changed by running pm2 restart app.json --env DEV|DEVPI|PRODUCTION
• updated scripts/switch_env.sh to use the new approach to ENV swticing
• in devices/controller/temperature/Temperature.js put require('mcp-spi-adc') in a conditional to prevent error in Vagrant environment