remove need to have blank left nav partials

the simple way I used to customize the left nav requied that each
section have a partial for the left nav, but most of them were blank.
now the empty partials don't have to exist.
replace twitch with tumble is page nav

I haven't streamed much at all lately, and there isn't any content of
mine on twitch at the moment, so tumblr is a better bet.