Fixed mesh loading when url has a query string

When loading a mesh using SceneLoader.ImportMesh, if the URL had a query string, it was considered as part of the extension, so it was looking for a plugin to load ".babylon?foo&bar" files.

I just changed it to take the extension from between last dot and first question mark.

PS: the gulp build from typescript fails for me, had to do it manually (build from js works) :)