Objective-C layer

I'd like to add a layer to spacemacs for using Objective-C. Right now there isn't that much I envision this layer doing, mostly some magic-file-alist stuff to determine whether a .h file is obj-c or c/c++ and some general filetype associations.

Later on it would be possible to add support for compile through xcrun and more.

I'd be willing to work on this, but I'd like to hear from others if this is something that might be useful or if there are any other ideas.