Don't set un-parseable numbers to 0 in the config

Previously if an integer or float field was empty it would
default to zero instead of undefined which made it inconsistent
with string value fields.

Now the config value is only set as a Number when it can be
parsed as one.

spec/app/config-panel-spec.coffee

@@ -42,6 +42,19 @@ describe "ConfigPanel", ->
     panel.stringInput.val('moo').change()
     expect(config.get('foo.string')).toBe 'moo'
 
+    panel.intInput.val('abcd').change()
+    expect(config.get('foo.int')).toBe 'abcd'
+
+    panel.floatInput.val('defg').change()
+    expect(config.get('foo.float')).toBe 'defg'
+
+    panel.intInput.val('').change()
+    expect(config.get('foo.int')).toBe undefined
+    panel.floatInput.val('').change()
+    expect(config.get('foo.float')).toBe undefined
+    panel.stringInput.val('').change()
+    expect(config.get('foo.string')).toBe undefined
+
   it "automatically binds named editors to their corresponding config keys", ->
     class TestPanel extends ConfigPanel
       @content: ->
@@ -73,10 +86,17 @@ describe "ConfigPanel", ->
     expect(config.get('foo.float')).toBe 3.3
     expect(config.get('foo.string')).toBe 'All limitations are self imposed.'
 
+
     panel.intEditor.setText('not an int')
     panel.floatEditor.setText('not a float')
+    window.advanceClock(10000) # wait for contents-modified to be triggered
+    expect(config.get('foo.int')).toBe 'not an int'
+    expect(config.get('foo.float')).toBe 'not a float'
+
+    panel.intEditor.setText('')
+    panel.floatEditor.setText('')
     panel.stringEditor.setText('')
     window.advanceClock(10000) # wait for contents-modified to be triggered
-    expect(config.get('foo.int')).toBe 0
-    expect(config.get('foo.float')).toBe 0
+    expect(config.get('foo.int')).toBe undefined
+    expect(config.get('foo.float')).toBe undefined
     expect(config.get('foo.string')).toBe undefined