Various fixes to RCTView props

[aleclarson]

Fixes #232

• move [RCTViewManager checkLayerExists:] to [NSView ensureLayerExists]
• enable edge antialiasing only for transforms with perspective
• stop setting layer manually in [NSView ensureLayerExists] (let the layer getter call [NSView makeBackingLayer] instead)
• never set layer.transform directly except in [RCTView displayLayer:]
• call ensureLayerExists before setting any layer-related prop
• call ensureLayerExists inside reactSetFrame: so layer props can be set
• enforce position and anchorPoint by setting them in [RCTView displayLayer:]
• fix [RCTView setBackgroundColor:] strangeness