New MRC request icon

This replaces the temporary MRC request contract icon with the
winner of the icon poll on mainnet. See

https://www.reddit.com/r/gridcoin/comments/v3suih/mrc_icon_poll/

The poll id is

4e3e06e88c5315eff95365a40d3a12d7dbd14205dc775c645c9f8b9dd2e99dc9

The winning icon is #7.

Many thanks to m3prx for contributing the winning icon! :)

Author: jamescowens