System browser redesign

The idea is to visually simplify the system browser to make the browser more attractive. Main issues addressed are: 
- Command Buttons consume much space, but are typically only of little use -> integrate the commands into the window's menu
- the source input line (below title bar) is also distracting and consumes too much space -> make the sourceInput edit control smaller so that it fits above the left pane; integrate the buttons 'Codebase' and 'Local' into a context menu for the edit control
- avoid transparency and gradients (rather distracting, and only of little use)
- further smaller layout improvements ..

Before:
![browser_before](https://f.cloud.github.com/assets/4905369/742107/d3f4c7c8-e3c0-11e2-805e-714379208534.png)

After:
![browser_after](https://f.cloud.github.com/assets/4905369/742110/d9e9464a-e3c0-11e2-9859-2e639fd2ab99.png)


Upcoming improvements:
To introduce a third view or state for the browser, in addition to the regular full view and the collapsed view only showing the title bar. The additional view will only show the source code editor and the title bar, but not the navigation bar (list panes). This view/state will be of use when users want to keep some piece of source code visible on the screen but no longer need the navigation features. See below ...

![browser_design](https://f.cloud.github.com/assets/4905369/742159/eec429b2-e3c1-11e2-83d1-73bfa1456574.png)