R1:6f1dfbb658a4

Paste - kill tabs

Summary:
merge paste create and paste list into a single controller. Add a "filter list"
to the left hand side and have new "create w/ recent", "my" and "all" views. UI
wrinkle -- "create w/ recent" does not paginate the recent pastes and instead
upsells the user to the new "all" view.

Also includes a business logic clean up or two for simplicity of code.

Test Plan:
- created a paste from the UI
- tried to create a paste with title and no body
- tried to create a paste with no title…