Automatically convert between ArrayHandleBasic and ArrayHandleRuntimeVec

The UnknownArrayHandle has been updated to allow ArrayHandleRuntimeVec to work interchangeably with basic ArrayHandle. If an ArrayHandleRuntimeVec is put into an UnknownArrayHandle, it can be later retrieved as an ArrayHandleBasic as long as the base component type matches and it has the correct amount of components. This means that an array can be created as an ArrayHandleRuntimeVec and be used with any filters or most other features designed to operate on basic ArrayHandles. Likewise, an array added as a basic ArrayHandle can be retrieved in an ArrayHandleRuntimeVec. This makes it easier to pull arrays from VTK-m and place them in external structures (such as vtkDataArray).

Fixes #752 (closed)