Switch to bower for client assets.

fixes #2272
- Remove libraries from shared/vendor
- Remove libraries from client/assets/vendor
- Add bower to package.json and postinstall
- Add bower.json with dependencies
- Add scripts from bower_components to concat/uglify
- Fix tests
- Serve jquery from /ghost/built/theme/
Merge pull request #2326 from halfdan/bower

Switch to bower for client assets.