Remove MahApps.Metro as git-submodule
Squashed 'MahApps.Metro/' content from commit 5509b1c

git-subtree-dir: MahApps.Metro
git-subtree-split: 5509b1cc1babf7cda2f4b3fa41c805f40e51b9ff
Merge commit '7bfa1e2e0ac56b797ab1f4f7896cde209c22ce02' as 'MahApps.Metro'
Add MahApps.Metro as git-subtree