Add API modifiers to limit returned toots from public/hashtag timelines

to only those from local users; Add link to "extended information" to
getting started in the UI; Add defaults for posting privacy; Change
how publish button looks depending on posting privacy chosen

app/views/home/initial_state.json.rabl

@@ -1,24 +1,24 @@
 object false
 
-node(:meta) {
+node(:meta) do
   {
     access_token: @token,
     locale: I18n.locale,
     me: current_account.id,
   }
-}
+end
 
-node(:compose) {
+node(:compose) do
   {
     me: current_account.id,
-    private: current_account.locked?,
+    default_privacy: current_account.user.setting_default_privacy,
   }
-}
+end
 
-node(:accounts) {
+node(:accounts) do
   {
     current_account.id => partial('api/v1/accounts/show', object: current_account),
   }
-}
+end
 
 node(:settings) { @web_settings }