.osx: Add Activity Monitor settings
.osx: Add Messages settings

* Use plain text smileys in Messages

  Messages in OS X 10.9 Mavericks automatically substitutes
  e.g. `:)` with `😊``, with no way to disable this feature
  through the app’s preferences pane.

  After analyzing the `defaults read` output it turns out
  there is a hidden preference for it.

* Disable smart quotes in Messages.app

* Disable continuous spell checking in Messages.app
.osx: Allow installing Chrome user scripts via GitHub Gist or Userscripts.org
.osx: Disable the all-too-sensitive backswipe on Chrome
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