Use material design list formatting for session and project lists

[dantman]

https://www.google.com/design/spec/components/lists.html

session/project lists are expandable lists, the material/paper formatting doesn't work right in this context.

Instead use the behaviour recommended for lists with expandable content:

• No elevation shadows or extra margins
• Style like a flat list of items
• When an item is expanded show a divider appears above and below the item

[agektmr]

Thanks @dantman for the PR. I can't judge this right away due to lack of Material Design knowledge. Give me some time then I will get back to you.