Implement Travis CI builds

[jonnenauha]

So we can get a badge of current build status (if people want could report to the rex irc channel too). And can see the build state on each commit.

Something like this from the top of my head.

// VM init
apt-get install nodejs // is npm installed with this on linux or needs another package?
npm install -g bower grunt-cli

// build
git clone
npm install && bower install --allow-root
grunt build
grunt doc

Add status badge to readme.md