Added configuration options to Jobs Grid with icons dashboard portlet

Hi,

Those modifications are based on a pull request I made for the legacy Jobs Grid portlet. They add:
- An option to configure the number of columns
- An option to fill columns first
- An option to choose the icon size.

![customiconconfig01](https://f.cloud.github.com/assets/1243537/79987/ff5471de-61e3-11e2-810b-2df235433d2f.png)

![customiconconfig02](https://f.cloud.github.com/assets/1243537/79988/0353b2b8-61e4-11e2-991e-093a89450afa.png)

Note: when updating the plug-in, the portlet is empty. The user have to edit the view and save it to bring back the grid.

Cheers,
syl20bnr