Fix look of Contact Page for partner First Name

Remove the "Is a company?" option in Partner's Contact Form as these are never companies

## Vanilla
![capture d ecran de 2014-11-05 17 42 04](https://cloud.githubusercontent.com/assets/1013356/4927639/57b6ae2e-653d-11e4-8402-4a1ecd04546f.png)
![capture d ecran de 2014-11-05 17 41 52](https://cloud.githubusercontent.com/assets/1013356/4927640/59281d56-653d-11e4-8744-6e9ce0084a52.png)
## Current implementation
![capture d ecran de 2014-11-05 17 41 29](https://cloud.githubusercontent.com/assets/1013356/4927646/5fea64a0-653d-11e4-9856-19c028d1241f.png)
![capture d ecran de 2014-11-05 17 41 15](https://cloud.githubusercontent.com/assets/1013356/4927647/6125e308-653d-11e4-8c6a-ca44d9af52aa.png)
## Fixed look
![capture d ecran de 2014-11-05 17 57 31](https://cloud.githubusercontent.com/assets/1013356/4927869/33777bcc-653f-11e4-967b-746bbb86b742.png)
![capture d ecran de 2014-11-05 17 57 43](https://cloud.githubusercontent.com/assets/1013356/4927867/3245f5ee-653f-11e4-8e55-49fa5f37d0ee.png)


Instead of making a replace, you can use:
```
<xpath expr="//form[@string='Contact']/sheet/div/label" position="attributes">
    <attribute name="invisible">1</attribute>
</xpath>
```