Add easy way to disable inventory tracking.

Currently inventory is always being tracked (resulting in backorders if not replenished).
This PR adds a simple NoopInventoryOperator and a configuration switch.
Add Customer Welcome Email
Nesting email settings & configuration
Add security step event
Add OrderUserListener to cart initialize event
Merge pull request #878 from Richtermeister/customer-welcome

Add Customer Welcome Email
Add EventListener to complete Order
Add post creation Order events
Set OrderShippingState to checkout by default
[TaxonomiesBundle] Cleanup models to match latest changes
Reduce Travis-CI build on main repository to only master branch
Translate address stuff
Translate personal home stuff
Translate order stuff
Translate general stuff, blocks and breadcrumbs
Translate exchange rates
Translate frontend stuff
Translate payments and promotions
Translate taxonomies
Translate user stuff