[Feature Request] Add support for PLY files

[ClemensU42]

Additional context http://paulbourke.net/dataformats/ply/

[GaryHuan9]

Follow the .ply specification and create a loader for the file format. Additional notes:

• The loader can be situated somewhere in the Echo.Core.InOut namespace.
• Note that the .ply has both an ASCII format and a binary format. Let us work towards the ASCII format first and place the binary format as a future goal to support larger mesh files.
• Do not worry about multithreaded loading for now.
• Do not place everything in the constructor. The constructor should only construct the loader, use separate methods to perform the actual loading :) structure this loader similar to the BinaryReader class but we are able to traverse up and down within the file.
• The loaded data can be in a custom format for the loader (for now), when we integrate it with Echo.Scenic (through the .echo format) we will need to translate it into PreparedTriangles.
• The Echo.Scenic system will support reading from streaming data. This mean that if file.ply has 1 million triangles, we should not load all of it into memory at one time. During preparation phase, Echo.Scenic will request data to be streamed from file.ply and progressively loaded into the prepared scene.
• Try to see if there is a way to get/calculate the number of triangles that will be loaded. This is to better support the streaming system. If the exact number cannot be determined, we can figure out a way to find the upper approximation.

The reason that we want a new mesh loader targeting the .ply is to prepare for the incoming .echo scene file. One of the biggest features the .echo file will have is its ability to do lazy loading. Information is loaded at the latest point when they are needed and metadata (such as triangle count from .ply files) will be used to direct PreparedScene construction and other heuristics to better utilize multiple cores on a large scale.