Add a loading GIF to show a query is running

[ColinMaudry]

That should be present:

• when clicking Test in New and Edit mode
• when opening the View mode

Also, the Test button should be disabled when the query is running.

[ColinMaudry]

Probably these pure CSS animations: https://github.com/ConnorAtherton/loaders.css

[ColinMaudry]

This one! http://codepen.io/SoufianeLasri/pen/XmyzGg

And a long query to test it (thanks @innovimax https://twitter.com/innovimax/status/790905094208225281):

# Endpoint: https://query.wikidata.org/bigdata/namespace/wdq/sparql

SELECT (sum(?statmt) as ?sum) WHERE {
   [] wikibase:statements ?statmt
}