[WebProfilerBundle] Fixed form icon in toolbar

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

Usage of same form icon in toolbar than the one in sidebar, plus lossless compression of icon.

Before : 
![form-before](https://f.cloud.github.com/assets/77759/1750792/652c719e-65b4-11e3-9797-81bd87252515.png)

After :
![form-after](https://f.cloud.github.com/assets/77759/1750793/6d616a7c-65b4-11e3-8306-5e00ff1c9aa4.png)