UI improments, initial release

[forrestbao]

Here are some UI improvements to be done in preparing for initial release.

Must-have:

• A modern dashboard displaying user projects as cards or list elements, as in Google Docs, Figma, or Vercel. And a prettier button to create new projects. See Vercel's at here and here.
• Clean up the left banner. If certain information there is not useful to users, remove it. Only display those useful to users and debugging. Improve UI (nav bar and canvas sidebar) #34
• Clean up the horizontal navigation bar as well. Can we hover the user icon over the canvas? In this way, we maximize the workspace. Improve UI (nav bar and canvas sidebar) #34
• Remove hash ids from pod. If possible, allow users to name pods.
• Attach the output of a pod to its left or bottom, and allow the output to be collapsed and resized. Better output layout #50
• Change the border of a pod to shadowed. Use two different background colors for a pod and its output, like in Deepnote Better output layout #50
  
• Toggle control to display line numbers in a pod. #37

Stretchy:

• Display a + sign button below or right of a pod to prompt users to add a new pod to the right or down.
• Allow users to anchor a pod relative to another pod. So if the anchored pod moves, the anchoring pod moves with it.
• Automatically pushes away a pod if the expansion of another pod's output overlaps it.

[lihebi]

#34 cleanups navbar and sidebar. The navbar is small, so we probably don't need to fold it.