add contacts dir, leave mail files as is

- restructured storage.lua so reading/writing json is not duplicated
- when a player joins and has no contacts file yet, automatically add all players he wrote to

migrate.lua

@@ -4,6 +4,7 @@
 mail.migrate = function()
 	-- create directory, just in case
 	minetest.mkdir(mail.maildir)
+	minetest.mkdir(mail.contactsdir)
 
 	local file = io.open(minetest.get_worldpath().."/mail.db", "r")
 	if file then
@@ -23,3 +24,28 @@ mail.migrate = function()
 	end
 
 end
+
+
+mail.migrate_contacts = function(playername)
+	local file = io.open(mail.getContactsFile(playername), 'r')
+	if not file then
+		file:close()	-- file doesn't exist! This is a case for Migrate Man!
+
+		local messages = mail.getMessages(playername)
+		local contacts = {}
+
+		if messages and not contacts then
+			for k,message in pairs(messages) do
+				mail.ensure_new_format(message)
+				if contacts[string.lower(message.from)] == nil then
+					contacts[string.lower(message.from)] = {
+						name = message.from,
+						note = "",
+					}
+				end
+			end
+		end
+	else
+		file:close()	-- uh, um, nope, let's leave those alone, shall we?
+	end
+end