Handle null value

Should handle null value here, or promotions usage limit should not be nullable.
Merge pull request #2059 from MichaelMackus/promotion-handle-null-usage-limit

Handle null value
Update liipimaginebundle 1.0 completed
Merge pull request #2082 from antonioperic/upgrade-liipimagebundle-10

Update liipimaginebundle 1.0 completed
Add Subscription Bundle
Remove 2 file changes that are not related to this feature.
Simplify command code. Fix service configuration.
Refactor Subscription Processing Scheduling
Add SubscriptionEvent and introducing some new Events (Subscription Process Success, Batch Start, Batch End)
Fix incorrect reference to shipping bundle (bad copy&paste)
Fix SubscriptionItem::getProduct() without Variant
Remove unused classes (added by mistake). Fix access validation. Button up integration with User.
Add missing license headers. Tweak composer config. Make form subscriber class configurable.
Fix fixtures to not generate out of bounds reference
Updated authors & bumped sylius versions
Cleanup and other misc. updates from latest rebase
cs
Added subscription to composer files
Fix subscription unit tests and some cs
Version bump