[FEATURE]: Load external textures for .ply objects

[Sebastian-Jung]

Is your feature request related to a problem? Please describe.
Although the .ply format does not officially support texture files, many applications such as meshlab, CloudCompare and a few datasets in the BOP challenge allow comment TextureFile File.png in the header to allow for an texture image to be loaded. It also helps to generalize the BOP format.

Describe the solution you'd like
The current ObjectLoader does not support the comment TextureFile File.png option whereas the _BopLoader is able to do so. Moving the ability from the _BopLoader to the ObjectLoader would solve the issue.

Describe alternatives you've considered
Using .obj files with given .mtl files and textures. This works but adding more feature to loading .ply objects shouldn't be bad.

Additional context
Related to #790

[Sebastian-Jung]

I will work on it.