Separate some methods about touch from `motion/joybox-ios/core/layer.rb` for mix-in to other Layer class

This issue was #54. create new pull request by my git push mistake.

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i suggest to separate some methods about touch  from `motion/joybox-ios/core/layer.rb`.

i add `layer_touchable.rb`. and mixed-in from `layer.rb` and new `layer_color.rb`
This enable also LayerColor instance to be receive some methods for touch.

i couldn't find such module for mix-in in sources.
so this  module name and location may be bad for your convention.

please consider.