Lighter tab bar look to match rest of UI

Purpose of this patch is too create bit lighter look of tabbar, so it plays nicely with new UI (and other my patch of having tab bar above document only)

This is just subtle modification of `TabBar.plist`.

**Proposed:**
![proposed](https://f.cloud.github.com/assets/103067/92144/14f9a782-65bf-11e2-982e-69106f225179.png)

**Was:**
![was](https://f.cloud.github.com/assets/103067/92145/19034f86-65bf-11e2-8523-27c0e700ed7b.png)