Bug 830644 - [Contacts][Hidpi]Support high resolution devices

* Added @2x assets
* Added background-size declarations
* Added support for high resolution profile pictures (facebook+contacts)
* Some JS additions to handle drag effect in different devices
* Removed `responsive.js` as we are using a shared css file to handle multi-devices UI

This PR has been created from this source: https://github.com/mozilla-b2g/gaia/pull/8939
Please @jmcanterafonseca and @albertopq take a look.