[GEOS-5907] Add Legend panel to CSS demo

This one uses legend decorations (which are added automatically to the data dir) to show the legend in a scale dependent manner:

![zoom1](https://f.cloud.github.com/assets/325433/933161/f459b594-0050-11e3-9549-18df6e4a3d68.png)

![zoom2](https://f.cloud.github.com/assets/325433/933160/f459d4fc-0050-11e3-8a1b-4ec8b15ecfdc.png)

Hmmm... the way titles are combined needs work, this way they get long, and they are combined in a english specific way (title1 with title2)