Replace `/api/externalprofile/show.json` with a MastoAPI equialent

/api/v1/accounts/:id supports remote nicknames since pleroma!1622 (merged)

src/components/who_to_follow/who_to_follow.js

@@ -26,7 +26,7 @@ const WhoToFollow = {
         }
         this.users.push(user)
 
-        this.$store.state.api.backendInteractor.externalProfile(user.screen_name)
+        this.$store.state.api.backendInteractor.fetchUser({ id: user.screen_name })
           .then((externalUser) => {
             if (!externalUser.error) {
               this.$store.commit('addNewUsers', [externalUser])