I can show and hide jqGrid columns

related to: https://github.com/9ci/grails-angle-grinder/issues/47

- [x] create basic example
- [x] simple public API for showing and hiding columns
- [x] discover how it's implemented in jqGrid
- [x] create a dialog for show and hide selected columns
- [x] ability to specify grid id (it could be used for persisting column model for later usage)
- [x] spike: persist selected columns in the local storage
- [ ] design and implement service for storing and retrieving column model from the local storage
- [ ] use this solution for other grids
- [ ] fix grid columns resizing issue