Created placeholder class

TO BE IMPLEMENTED. Necessary for MysticalModelCenterCalculator.
Added a constructor and conversion function.

The new constructor takes a Vec3 as input and initializes the 4th
component to 0.
The new function converts a Vec4 to a Vec3, discarding the 4th
component.
Removed ungly try-catch hacks.

The functions that throw exceptions no longer catch the exceptions
themselves.
Removed fiducialCoordinates attribute from SmartBlock. Moved it to Block.
Added fiducialOrientation attribute to Block
Further implementation of MysticalModelCenterCalculator

The MMCC has gotten so far as to move d to the origin, align model and
world d and make a new vector space with d, offset and their cross
product a basis.
We next need to find the model center in d-space so that we can
eliminate half of the possibilities easily.
We then need to do the part that converts orientations back to world
space.