CCEditBox iOS enchantments/bugfixes

1. Allow to set fontName and fontSize for placeholder separately. This ability have a few use cases, but most notably it allows to load CCEditBox using CocosBuilder plugin. I'm currently working on one and I'm going to open source plugin and loader when it will be ready.
Not sure if I should send PR with a plugin to CocosBuilder repo: cocos2d-iphone have no edit box control. Will be glad to know your and @vlidholt opinion on this topic.

2. Correctly resize the subnodes and native text field when CCEditBox's contentSize changes.