Fix memory alignment in loading meshes

[jslee02]

This pull request addresses the memory alignment issue with Eigen object in loading meshes, which was reported by @jturner65 in #599.

[mxgrey]

The changes look good 👍, but is there a particular reason that VS can't compile it in release mode? Is it just timing out?

[jslee02]

Hm, I'm not sure. Let me make AppVeyor test it again, and test it myself on my virtual machine in parallel to figure it out. I tested it only for debug mode.

[jslee02]

I got an error as:

c:\golems\include\eigen\src\core\assign.h(527): fatal error C1002: compiler is out of heap space in pass 2

It seems it needs too much heap memory for 32 bit Windows to build DART. One possible solution would be optimizing the header inclusion as the suggestion of the first answer in this post.

[mxgrey]

It's very likely that our header organization could be improved dramatically, although I'm afraid it might require some refactoring of classes, such as decomposing them into simpler classes and carefully sorting through the dependencies between them.

I don't know who would have time to actually do that, or when.

[jslee02]

Yeah, we should give it a try to improve the header organization at some point, but not now. I'm merging this PR, and creating a new issue for this build failure that might be related to the header organization.