[ToolBar] Add Center Items in ToolBar option

- Add Center Items in ToolBar option (nice for Big screen resolutions).
- Update Translations.
- Add QCheckbox in Preferences general (defaults to False).
- Works OK on Horizontal position.


![temp](https://cloud.githubusercontent.com/assets/1189414/3021760/82de62e0-dfb9-11e3-9414-b6de2ce3f24a.jpg)


Brancho:  feature/center_toolbar  :octocat: