New Flood IF on OSM Building

Hi @Charlotte-Morgan @timlinux @cchristelis @mbernasocchi, this PR:
- addresses https://github.com/AIFDR/inasafe/issues/1237. So, if the hazard is raster, it will categorise the impact layer into 3 categories: inundated (equal or above threshold), wet (below threshold but not dry), and dry. The impact layer will look like: 
![new_if](https://cloud.githubusercontent.com/assets/992519/4626406/ba3cd1d2-5380-11e4-9eeb-61f67f66d913.png)
- Please give some feedbacks on the impact layer style and the name for each category.
- This PR needs translation updates
- I assume there are a lot of failing tests (will look at it if you are all happy with this result)
- After you're happy with this changes, I will duplicate this for Tsunami On Building IF to address #1238   and #502 (Name of Tsunami Impact Function is not valid)