[FEATURE] extend item table with currency-change functionallity

__Requires:__
- https://github.com/sulu-cmf/SuluProductBundle/pull/67

__Tasks:__
- [x] done
- [ ] got feedback

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | none
| Doc           | none

use constants