Display shipping methods for ALL matching zones on checkout
rename output for css assets

In a production environment, when trying to dump the assets, for some reason if the name of the output is backend.css (same of the layout.html.twig), it is overwritten by this and the blueimp gallery is lost.
In the dev environment that doesn't happen.
Renaming the output to something else fixed it for me.
Add missing addDefaultsIfNotSet() calls

An addDefaultsIfNotSet() method is not called on every array element of config tree. As the result, config is not properly populated with default values.
Merge pull request #1185 from 20th/master

Add missing addDefaultsIfNotSet() calls in InventoryBundle config
Modify _variant.html.twig in order to be able to see images at generated pdf invoices
ability to close alert box
Merge pull request #1145 from foopang/fix/issue-1145

Not able to select a shipping method where there are both shipping zone and product restricted zone that match user's shipping address
Added parameter 'true' to imagine filter
Add validation when saving parameters to guarantee database integrity
Fix missing use statement
Adding CONTRIBUTING.md file

Inspired by blog post: http://sylius.org/blog/contributing-guide
Merge pull request #1189 from JRomeoSalazar/pdf-images

Images at PDF format invoice
Merge pull request #1176 from fourlastor/patch-1

rename output for css assets
[SettingsBundle] Reduce code duplication across bundles
Merge pull request #838 from stloyd/feature/settings_duplication

[SettingsBundle] Reduce code duplication across bundles
Synchronize Crowdin translations
Improvements for parameter validation
Change value type of Parameter to object
Merge pull request #1194 from SyliusBot/feature/sync

Synchronize Crowdin translations
Cosmetic fix in Settingsmanager