Added support for BIGINT UNSIGNED type in MySQL and MariaDB DBTypes

[AndreiKingsley]

Fixes #762.

[Jolanrensen]

could you add tests for this specific fix? :)

(the build should not have failed, I'll rerun)
(okay, maybe rebase on master, I've limited the maven logs, they were getting way too large)

[AndreiKingsley]

@Jolanrensen added tests as an initiating of #1736.

[Jolanrensen]

@AndreiKingsley that's good :) though, I would also recommend running a test with the actual database, like here https://github.com/Kotlin/dataframe/blob/c3742a95684d53a813d978a3c895090ba684c46e/dataframe-jdbc/src/test/kotlin/org/jetbrains/kotlinx/dataframe/io/local/mysqlTest.kt (though, you'd need to set up a local database for that. Just ask Junie to do that for you ;P, I think @zaleslaw would appreciate it :) )

[AndreiKingsley]

@Jolanrensen , added BIGINT UNSIGNED columns to Genereal MariaDB / MySQL tests!