core: Start folsom in boot sequence

Otherwise Zotonic crashes on startup with:

21:01:38.682 [error] CRASH REPORT Process <0.173.0> with 0 neighbours exited with reason: bad argument in call to ets:member(folsom, {zotonic,webzmachine,requests}) in folsom_ets:handler_exists/1 in gen_server:init_it/6