Implement thread archiving

[Circlepuller]

Archiving is now considered a standard feature on most imageboards and I feel it's time we should implement it in some way. NPFchan has done it but I feel we could definitely work out some quirks that it seems to have..

[Circlepuller]

As of ff4cd3d, a majority of the archive code has been implemented, and most of what still needs to be done is the HTML templating and moderation functions. Any constructive criticism or commentary on this feature update is appreciated.

I'd also like to credit the contributors behind NPFchan for creating a basis for this functionality.