Line-up tab bar height with file browser header

1st commit: Slightly enlarging tab bar height so it seamlessly integrates with file navigation header.
2nd (optional) commit: Bumps little bit lightness of tab bar as it is hardly readable right now (above new vs below old).
3rd (optional) commit: Makes tab bar labels bold like in other apps: Xcode, Safari.

@sorbits I know @infininight is in charge of the design, so these are just temporary changes to line up with tabs above document. And if you don't want to merge them, fine. At least anyone impatient like me would be able to merge these out of this ticket from my branch and build TM version with stuff properly aligned.

Look after the changes:
![now](https://f.cloud.github.com/assets/103067/114881/731fbb7c-6bb8-11e2-9336-5926ac35ce42.jpg)

Before:
![was](https://f.cloud.github.com/assets/103067/114883/77cb6fb8-6bb8-11e2-9067-e10ca1923435.jpg)