Update podspec to add UI component as a subspec

Refactor core component into a subspec.

Note all subspecs are included in the root spec if
default_subspecs isn't specified.
Rename UI component asset catalog to prevent collisions

Note this won't be necessary when our podspec
exports a custom resource bundle, but that would
complicate keeping NBClientExample in the same
workspace. Also, with included further
optimization via ImageOptim, our resource bundle
size is relatively small (<200kb). So custom
resource bundles are tabled for now.
Update podspec to add locale component as a subspec
Merge pull request #30 from 3dna/peng/podspec-2

Add podspec #2

Complete podspec with additional components by
using subspecs. Minor renaming and optimization
included.