Add method to clear variants registry

app/assets/javascripts/darkswarm/services/variants.js.coffee

@@ -1,6 +1,10 @@
 Darkswarm.factory 'Variants', ->
   new class Variants
     variants: {}
+
+    clear: ->
+      @variants = {}
+
     register: (variant)->
       @variants[variant.id] ||= @extend variant
 

spec/javascripts/unit/darkswarm/services/variants_spec.js.coffee

@@ -23,3 +23,9 @@ describe 'Variants service', ->
 
   it "initialises base price percentage", ->
     expect(Variants.register(variant).basePricePercentage).toEqual 81
+
+  it "clears registered variants", ->
+    Variants.register(variant)
+    expect(Variants.variants[variant.id]).toBe variant
+    Variants.clear()
+    expect(Variants.variants[variant.id]).toBeUndefined()