Fix saving error of video editor with non-english translations

Currently the code in ```tabs-aggregator.coffee``` uses the display name of a tab as the key to index the current tab. When a non-english translation is applied, the javascript code will get localized names instead of the original english names, which causes the ```getValue``` function fails as it cannot reference the correct tab.
Here I use the ```data-tab_name``` attribute to store the original english tab name, so it can be later used as the index key.