Fix for #1314 - Register/Sign Error Page & Style issue

Just checked this issue: https://github.com/NuGet/NuGetGallery/issues/1314

With Opera 21.9  this issue is obsolete, but I found a related issue, which occurs on all browsers:
![image](https://cloud.githubusercontent.com/assets/756703/3109458/b3181a96-e699-11e3-85db-3b80a3c4a879.png)

Reason for this is the fixed position of the validation messages via CSS. 

My simple solution: Delete the position: absolute rule plus some cosmetic and everything should be fine:
![image](https://cloud.githubusercontent.com/assets/756703/3109483/072a9f0a-e69a-11e3-9b1d-52bb7580a83e.png)

The style is also used on the Package Edit Page which now looks like this:
![image](https://cloud.githubusercontent.com/assets/756703/3109494/2c8c109e-e69a-11e3-8c66-dacea8740641.png)

And the support page:
![image](https://cloud.githubusercontent.com/assets/756703/3109507/4201194c-e69a-11e3-82ce-6a33da510b09.png)

The Account and VerifyPackage pages have similar forms as well.

As you can see the validation message has currently a fixed size, but with the redesign there might be a bigger change coming anyway and maybe there will be a "standard" size for inputs, thats why I leave it as is.