Fix Instagram and add Glui image loading

Images shared with Instagram nearly always end with a slash (when shared via the client), but of course it's possible for someone to copy and paste one without (e.g. http://instagram.com/p/j4k_ZioaCo) as NASA recently did (https://twitter.com/NASA/status/429688471423156225) which was spread far and wide. 

URLs without trailing slashes weren't showing the images. Here's a fix.

Also, I've added image loading for glui.me URLs. Glui is a Mac app for easily sharing (and annotating) screenshots via Dropbox. For example, the code now changes:
http://glui.me/?i=98tadpgxfk2zudn/2014-02-01_at_16.20.png/
into:
http://dl.dropboxusercontent.com/s/98tadpgxfk2zudn/2014-02-01%20at%2016.20.png

Tested on Symbian (Nokia 808) and checked Harmattan builds.