replace with Cocoapods

@corinnekrych here is branch that replaces .gitmodules with cocoapods. Since it requires the 'swift' branch we utilise Gem to install a local copy without affecting the system installed one. Curently the ```Podspecs``` for each respective library resides in the private ```podspec``` branch and If we are happy with it, will open PR to merge with `master'

To test, cd to each cookbook and: 

```
bundle install
bundle exec pod install
```