Update npms hubot, hubot-flowdock, hubot-scripts; add "engines" section to package.json

Taken from a new hubot instance (generated by hubot 2.4.8)
Update scripts for 2.5.1

Just copied them from node_modules/hubot/scripts.
Update and improve our scripts for new hubot version.
fixup package.json
Add some more scripts.
Unignore node-modules.