Use event methods for theme subscriptions

spec/atom-spec.coffee

@@ -520,7 +520,7 @@ describe "the `atom` global", ->
 
             reloadedHandler = jasmine.createSpy('reloadedHandler')
             reloadedHandler.reset()
-            atom.themes.on('reloaded', reloadedHandler)
+            atom.themes.onDidReloadAll reloadedHandler
 
             pack = atom.packages.disablePackage(packageName)
 

src/atom.coffee

@@ -373,7 +373,7 @@ class Atom extends Model
     @themes.load()
 
   watchThemes: ->
-    @themes.on 'reloaded', =>
+    @themes.onDidReloadAll =>
       # Only reload stylesheets from non-theme packages
       for pack in @packages.getActivePackages() when pack.getType() isnt 'theme'
         pack.reloadStylesheets?()