Added Altar, as a generic block for now,
It cannot be placed with a block around or above it, however if you place a block above it or around it it will break. A bug is you can place it on itself (above) and the bottom will break also the corners after it is placed will allow people to add a block.
A feature I added was that will detect the light level and adjust it acordingly, so if it is bright where it is placed it will emit no light, but if it is dark then it will produce light.