Add support for scopes

- Add scope selection for for new post
- Save new post scope in db
- Copy scope on reply
- Show scope icon on posts

model/postContext.go

@@ -0,0 +1,12 @@
+package model
+
+type PostContext struct {
+	DefaultVisibility string
+	ReplyContext      *ReplyContext
+}
+
+type ReplyContext struct {
+	InReplyToID   string
+	InReplyToName string
+	ReplyContent  string
+}