update rails master
FIX: Change is_staff to is_admin to match other places where guardian.allowed_category_ids is used
https://meta.discourse.org/t/security-permissions-and-messages-displayed-on-group-url/22169/17
Merge pull request #2971 from cpradio/pr-fix-allowed-category-ids-for-group-posts

FIX: Change is_staff to is_admin for group posts to match other places
PERF: use preloader trick to load topic categories
be explicit about log level
PERF: don't ever use inject on AR relations

inject will deteriorate to a method missing that
invokes arel and a world of uneeded work
fix minor typo
Omit Needless Words
specify max-width 100% on digest email logos
bump up header icon size a bit
FEATURE: new 'maximum new user accounts per registration IP' site setting
UX: whitelist OpenStreetMap iframes
FEATURE: improve admin IP lookup dialog (add username/trust level/read time/topics entered)
FEATURE: only limit new registrations from that IP if all the users from that IP are TL1 or TL0
Merge pull request #2973 from lidel/openstreetmap-support

UX: whitelist OpenStreetMap iframes
Merge pull request #2972 from intelliot/patch-1

fix minor typo
fix the build
FIX: changing category within edit grace period as TL3 pops up an error
fix the build (again)
FIX: do not display EPOCH