Fix types in database, add UserId, fix file usage in submission command.

highscores_database.sql

@@ -47,9 +47,10 @@ CREATE TABLE Scores(
 CREATE TABLE Submissions(
    CategoryId int unsigned not null,
    GroupId int unsigned not null,
-   GuildId int unsigned not null,
-   MessageId int unsigned not null,
+   GuildId bigint unsigned not null,
+   MessageId bigint unsigned not null,
    Score varchar(30) not null, -- Score is stored as a string until converted during submission
+   UserId bigint unsigned not null,
    UserName varchar(30) not null,
    PRIMARY KEY (CategoryId, UserName) -- one submission a category per user.
 );