(Bug 5265) Create skins/global-styles

Common point to @include anything that should be included for *all*
skins, so we don't have to edit all the skins for each new file
(Bug 5265) Tweak wording for community settings
(Bug 5265) Simplify /communities/new

* removes entry moderation / only-select-people-can-post options from
  the community creation screen (not often changed)

* adds "next steps" to the success screen, which links to edit settings
  / edit profile / customize community