Use archived links sitewide

Inevitably, some of the links being used around on the site (particularly, the slockit blog posts about hard fork) have been removed, so we should use archived links for these instead.

Rather than updating the links themselves we can do sitewide or section wide replacements automatically to some archive service such as wayback machine or archive.is.

Some of the links however are unfortunately not archived on all sites (for example the "send ether to ETC address" tutorial on medium that was deleted), ideally we'd be able to find a copy that was backed up somewhere or run a script to automatically figure out which archive is available.

I'll leave this here in case any has suggestions, and will look into it.