Add bower as package dev dependency

[franz-josef-kaiser]

As per the README, Bower is needed to fully set up the project. As not everyone has Bower installed and everyone might have a different version, I'd like to suggest to add it as development dependency and alter the README to run it via ./node_modules/.bin/bower install instead of calling some globally available alias. Thanks!

[volumio]

Upgraded the readme, thanks

In any case you are right that we should call the locally installed bin. A PR making that would be appreciated

[franz-josef-kaiser]

@volumio in case you reopen the issue, I can file a related PR.