Introduce list view to channels

[salieflewis]

• Ability to toggle between list view and grid view
• List view as the default view for channels
• Accessible contextual menu to:

1. Add an item to any channel
2. Get more information about that item
3. Remove that item from the current channel

Note

• Filtering items in this view need not extend to this PR.

[salieflewis]

Figma

Desktop: https://www.figma.com/file/vq8D56Fddhysfv24raCmL1/River?type=design&node-id=424%3A400&mode=design&t=EktodE7JS2SVIx8v-1

Mobile: https://www.figma.com/file/vq8D56Fddhysfv24raCmL1/River?type=design&node-id=655%3A464&mode=design&t=EktodE7JS2SVIx8v-1