Header/.m/.mm order clean up #416
Header/.m/.mm order clean up #416

Summary:
Moved .m and .mm files directly below header file for easier project
navigation.
Closes https://github.com/Instagram/IGListKit/pull/417

Differential Revision: D4430737

Pulled By: rnystrom

fbshipit-source-id: 6e67566c38c1804ce995ba48148734587cb93c74

Instagram/IGListKit,Instagram/IGListKit,Instagram/IGListKit,zhubofei/IGListKit,zhubofei/IGListKit,charles0126dev/IGListKit,zhubofei/IGListKit,charles0126dev/IGListKit,zhubofei/IGListKit,dshahidehpour/IGListKit,charles0126dev/IGListKit,Instagram/IGListKit,zhubofei/IGListKit,Instagram/IGListKit,dshahidehpour/IGListKit,dshahidehpour/IGListKit