Improved backend UI elements.

### Summary

I have updated the sidebar and some form element style. I believe this is a small step forward to make Sylius more polish, less bootstrap. This pull request focus entirely on UI element improvement and did not introduce any layout changes (no moving things around etc).

This also include some other minor UI fixes (title case etc).

Before:
![screen shot 2013-11-23 at 7 51 42 pm](https://f.cloud.github.com/assets/193112/1606367/af5c7bc8-5435-11e3-89d3-7a03baeb5942.png)

After:
![screen shot 2013-11-23 at 9 06 08 pm](https://f.cloud.github.com/assets/193112/1606465/11a7ce5e-5440-11e3-864d-c9d9f02567ee.png)

### Details

* Sidebar: Small font size to avoid word wrapping.
* Sidebar: All cap but smaller font in sidebar section header.
* Sidebar: Change highlighted / hover item style
* Table: Now includes a very light background. 
* Table: Lighter border.
* Icons: Removed Font Awesome and use Glyphicon instead as it is the icon font that comes with Bootstrap 3.
* Form elements: Thick border to match Sylius's bit font design.
* Buttons: Use Glyphicon as well.
* Buttons: Remove rounded corner.
* Buttons: Thick border, easier to tell which one is label and which one is button. Also match with text box style.
* Paginator: Update style.