Move images to src dir and clean up assets

[dcwalk]

@colinmccann -- I'm pretty sure I've cleaned up the img directory and moved appropriate files to src for minifying.

Can you confirm?

[colinmccann]

Yeah, spot checked this, looks right. I'm still a little queasy about having a separate dir for transparency img... what makes it so special? :)

[dcwalk]

Hey, do you not want merge these changes in? Would be good to proceed or choose another path to address. I was hoping to get this one "squashed and merged"

RE: transparency-- I'm not sure, happy to address via another commit

[colinmccann]

Bah, I swear I hit merge before closing. Sry!