Store chromecast_devices as proper objects in attributes

[bendikrb]

Storing this data as a string makes it impossible to use it in templates, in other words useless in my use case - where I want to use this data to populate an input_select;

{{ states.sensor.chromecast_devices.attributes.devices_json | map(attribute='name') | list }}

[fondberg]

Thanks för your PR. För backwards compatibility it would be best if you create a new attribute to store the objects and leave this as a string.

[fondberg]

Great! I'll test and release asap

[fondberg]

Needed some more small fixes and I can't access your branch so I added your fixes in #30 so I'll be closing this and releasing that