WIP: Common laplacians

Implemented an interface to compute per-vertex Laplacians. Currently there are two types of laplacians:

• Uniform Laplacian (all 1-weighted edges)
• Dual Laplacian (as described in the following paper: https://igl.ethz.ch/projects/LB3D/)

They share the same template-based interface which can be extended to other Laplacians.

Additionally, laplacians can either be computed at the construction of the laplacian class, or on a per-request basis.

The edge weights can also be accessed individually (to fill a Laplacian matrix for instance)