New configuration parameters to JobsPortlet

Hello,

Here is a pull request to add the following configuration parameters to JobsPortlet:
- Number of columns
- Fill column first

![JobsPortletConfig](https://f.cloud.github.com/assets/1243537/73879/b0b52fb0-6066-11e2-8c8b-30ad1244f829.png)

If "Fill column first" is checked then jobs are inserted from top to bottom then from left to right. It can feel more natural for some users.

![JobsPortletFillCol1st](https://f.cloud.github.com/assets/1243537/73880/b64d9890-6066-11e2-84d8-90623c7b3772.png)

Cheers,
syl20bnr