Add MangaDex login page

src/storage.cr

@@ -514,6 +514,37 @@ class Storage
     delete_missing "titles", id
   end
 
+  def save_md_token(username : String, token : String, expire : Time)
+    MainFiber.run do
+      get_db do |db|
+        count = db.query_one "select count(*) from md_account where " \
+                             "username = (?)", username, as: Int64
+        if count == 0
+          db.exec "insert into md_account values (?, ?, ?)", username, token,
+            expire.to_unix
+        else
+          db.exec "update md_account set token = (?), expire = (?) " \
+                  "where username = (?)", token, expire.to_unix, username
+        end
+      end
+    end
+  end
+
+  def get_md_token(username) : Tuple(String?, Time?)
+    token = nil
+    expires = nil
+    MainFiber.run do
+      get_db do |db|
+        db.query_one? "select token, expire from md_account where " \
+                      "username = (?)", username do |res|
+          token = res.read String
+          expires = Time.unix res.read Int64
+        end
+      end
+    end
+    {token, expires}
+  end
+
   def close
     MainFiber.run do
       unless @db.nil?