Create server side example

- [x] API endpoint for paged data
- [x] create grid example
- [x] implement server side sorting
- [x] implement server side updating
- [x] implement server side creating
- [x] implement server side deleting
- [x] cleanup the code
- [x] create separate module for edit item dialog
- [x] modularize other features (sample data generator, etc.)
- [x] write unit tests for the service
- [x] write specs for `ServerSideCtrl`
- [x] write specs for `AgGridDirectiveCtrl`