CSS for IDE UI

[RuizhePang]

Now the basic IDE UI is established, but it is not beautiful enough. CSS is necessary for beautifying the UI.
We use MonacoFX to build the editor, it provides two theme, 'light' and 'dark'. Base on this two themes, we need to write css files for other components.

Basically, several css files are required. Include but not limited to
fileTree.css
menuBar.css
bufferline.css
login.css
chatroom.css
and etc.