Bug 1364894 - Add missing image file extensions to url-loader
Bug 1364894 - Add missing image file extensions to url-loader

Neutrino 4 only configured `url-loader` for use with `.png` and `.jpg`.
This means that once we start parsing HTML properly in later commits,
we would otherwise get the following error:

```
ERROR in ./ui/img/dancing_cat.gif
Module parse failed: C:\Users\Ed\src\treeherder\ui\img\dancing_cat.gif Unexpected character '�' (1:6)
You may need an appropriate loader to handle this file type.
(Source code omitted for this binary file)
 @ ./ui/partials/perf/comparectrl.html 1:214-250
 @ ./ui/partials \.html$
 @ ./ui/js/cache-templates.js
 @ ./ui/js/perfapp.js
 @ ./ui/entry-perf.js
 @ multi ./ui/entry-perf.js
```

edmorley/treeherder,KWierso/treeherder,KWierso/treeherder,edmorley/treeherder,KWierso/treeherder,KWierso/treeherder,edmorley/treeherder,edmorley/treeherder