Make the config panel more compact

[Boshen]

I intend to add more options to the left hand side config panel.

I'm also wondering whether we should move the config panel to the right, as it feels more naturual, similar to most desktop apps? It's also easier to change settings when the tabs and configs are all on the right.

[sxzz]

Let's implement the config panel functionality first before focusing on aesthetics. After all, this isn't a user-facing website.