Support for Meshlab project format

Having support for the Meshlab (http://www.meshlab.net/) project formats (*.aln/*.mlp) would be great! And it should be fairly straightforward to do since they are just a list od ply-files with associated transformation matrices.

No files or tests are named. Start by locating Assimp's existing project or scene-format importers and their tests, then compare how they represent PLY files and transformation matrices. Done means both Meshlab .aln and .mlp project formats are imported with their referenced files and transforms handled correctly.

Written by the indexing model from the issue text.