Adds some minor tweaks.

- Adds a new property that can be used to set the blur intensity on the sky (current defaults to 100%)
- Fixes that motion blur with a blur intensity of 0 was active but almost invisible
- Adds various other properties to the Post Processing Renderer
- Adds new enum for various FBO types (more to come) to the Post Processing Renderer
Halves the amount of samples used for the light shafts post processing effect.
Adjusts luminance.
Added some extra checks into StringMapType serialization, so that null values are not serialized.
Fixed BlockChangedEvents not being sent when the player places a block.
Adds some more properties and tweaks all things related to HDR rendering (in combination with the recent post-processing effect additions).
Increased initial distance for dropped blocks and made inventories persistent for dropped blocks.
* increased distance to 2, blocks thrown away while looking down are no longer picked up directly
* removed deprecated method use
* store placedEntity for dropped blocks

Fixes #310
Merge pull request #443 from skaldarnar/develop

Increased initial distance for dropped blocks and made inventories persi...
Adds some more properties to the "sobel" edge detector shader and cleans up some other post-processing related things.
Fix for StringMap serialization.
Merge branch 'develop' of https://github.com/MovingBlocks/Terasology.git into develop
Terasology. New block family. Fences, rails and lader as bonus