VE-528, VE-530, VE-502: Uploading temporary files

https://wikia-inc.atlassian.net/browse/VE-528

@inez, please review.

ve.ui.Widget.css
Styling for icons inside of buttons

ve.ui.ButtonWidget.js
Modification to core. ButtonWidget now mixes in IconedElement. Adds icon if passed via config.

VisualEditor.i18n.php
Messages

VisualEditor.php
Export messages

ve.dm.WikiaCartItem.js
Extending model to contain temporary uploaded filename

ve.ui.WikiaMediaInsertDialog.js
Add upload widget to main page. Listens for successful uploads to update cart

upload.svg, upload-small.svg, ve.ui.Icons-vector.scss
New icons

ve.ui.WikiaMediaInsertDialog.scss
Styling for upload

ve.ui.WikiaMediaQueryWidget.js
Add upload widget and responsive layout wrappers. Methods to hide and show the wrapper around the upload widget.

ve.ui.WikiaUploadWidget.js
Handles selection and upload of images