Fix the rendering order of the challenges on the challenge page

[spMohanty]

The order of rendering for a challenge in the challenges page, and also on the featured challenges page, is dependent on a "feature sequence" no parameter, which you can manually set in the edit challenge page (the higher the sequence number, the higher the priority).

But its a pain to use when trying to arrange the order of multiple challenges.
Also, at the end of the challenge, it simply throws the challenge that ended to the end of this priority list.

An ideal interface would have a simple drag and drop interface to re-order the expected order of challenges.