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

* Added @2x assets (also new album covers at @2x)
* Added background-size declarations
* Removed mediaqueries for device screen and applied some `-moz-box-sizing` and `calc()` to fit in any screen width.
* Removed custom progress activity and updated with the real BuildingBlock

In order to test this PR you need to:
 * **HIDPI Device:** `HIDPI=1 make install-gaia` 
 * **non-HIDPI Device:** `make install-gaia` 
 * **B2G desktop:** run it with `--screen=480x800` flag

The source was: https://github.com/mozilla-b2g/gaia/pull/8861 Please @dominickuo take a look