Fix #277 -- Embeddable shop (#622)

* Vendor vue.js

* Refactor item_group_by_category to support vouchers

* Widget: Show product list

* Widget: free prices

* Widget: pictures and loading indicator

* Widget: First iframe steps

* Widget: Do not rerender iframe

* Widget: Error handling

* Improve widget

* Widget: localization tech

* Fix invoice style

* Voucher attribute and waiting list

* Add some iframe chrome

* First step to namespaced carts

* More isolation steps

* More cart isolation things

* More cart isolation things

* Mobile stuff

* Show cart on checkout pages

* PayPal and Stripe support

* Enable downloads

* Locale handling

* change text "save URL to this exact page"

* Widget: voucher redemption

* Widget: CSS

* CSS: Responsive

* Widget: CSS improvements

* Widget: Add embedding code generator

* Widget: Error messages and SSL check

* First tests

* Widget: tests

* Don't use IDs in widgets

* Widget: static files caching

.gitattributes

@@ -5,6 +5,7 @@ src/static/moment/* linguist-vendored
 src/static/datetimepicker/* linguist-vendored
 src/static/colorpicker/* linguist-vendored
 src/static/fileupload/* linguist-vendored
+src/static/vuejs/* linguist-vendored
 src/static/charts/* linguist-vendored
 src/pretix/plugins/ticketoutputpdf/static/pretixplugins/ticketoutputpdf/fabric.* linguist-vendored
 src/pretix/plugins/ticketoutputpdf/static/pretixplugins/ticketoutputpdf/pdf.* linguist-vendored