GEOS-5929: CSS demo page does not allow to style raster layers

Changed the code so that it refers to LayerInfo instead of FeatureTypeInfo, created a minimal data panel for raster data:

![editor](https://f.cloud.github.com/assets/325433/932629/a8bfa7b8-0043-11e3-838d-d2c48f5aed89.png)