Make project panel more compact

This ensures more deeply-nested entries can be displayed without
needing to show scrollbars. Adding scrollbars introduces UX issues
when creating/renaming files because there are two scroll layers:
the outer project panel AND the editor.

Sublime Text and Atom dodged this issue by not displaying an inline
editor and showing it as a modal instead. VS Code shows the editor
inline but has a much more compact visualization. I think we should
copy VS Code.

styles/src/styleTree/projectPanel.ts

@@ -6,7 +6,7 @@ export default function projectPanel(theme: Theme) {
   return {
     ...panel,
     padding: { left: 12, right: 12, top: 6, bottom: 6 },
-    indentWidth: 20,
+    indentWidth: 8,
     entry: {
       height: 24,
       iconColor: iconColor(theme, "muted"),