.gitconfig: Add `dm` alias

`git dm` deletes local branches that have been merged with master.

Closes #309.
init: Tweak Sublime Text settings
.osx: Add Activity Monitor settings
.osx: Add Finder ‘Get Info’ settings
Merge branch 'master' of https://github.com/mathiasbynens/dotfiles

# By Mathias Bynens (3) and Jarrett Drouillard (1)
# Via Mathias Bynens
* 'master' of https://github.com/mathiasbynens/dotfiles:
  .osx: Add Finder ‘Get Info’ settings
  .osx: Add Activity Monitor settings
  init: Tweak Sublime Text settings
  .gitconfig: Add `dm` alias

Conflicts:
	.gitconfig
	init/Preferences.sublime-settings