Methods to enable averaging multiple transform matrices

I wrote some methods to enable weighted averaging of multiple transform matrices in order to obtain a transform which is the "weighted midway" between the given transforms. To achieve this, translations are lerped and rotations are slerped. By definition, more than two Quaternions are slerped by:

```
(q_1^w_1)*(q_2^w_2)* ... *(q_n^w_n)
```

where `w_i` sum to 1. This is particularly useful when transform information from multiple observers must be combined into a single one.