Add property to Dev model
Add ButtonWidget in widgets.py
Merge branch 'master' of https://github.com/allegro/ralph into ralph_assets
Add api for device components for assets
Merge branch 'master' of https://github.com/allegro/ralph into ralph_assets
Add API assets
Raise LookupError in get_device_components
Merge pull request #552 from quamilek/ralph_assets

Add api for device components, get_components property on Device model and ButtonWidget in widgets added