Add a per-user setting to hide followers count

This is only available if the instance-wide setting isn't set and allows
people to hide their own followers count. This does not hide others' to
them.

config/locales/simple_form.en.yml

@@ -79,6 +79,7 @@ en:
         setting_display_media_show_all: Show all
         setting_expand_spoilers: Always expand toots marked with content warnings
         setting_favourite_modal: Show confirmation dialog before favouriting (applies to Glitch flavour only)
+        setting_hide_followers_count: Hide your followers count
         setting_hide_network: Hide your network
         setting_noindex: Opt-out of search engine indexing
         setting_reduce_motion: Reduce motion in animations