Increase gcheck numbers to 5 digits

[Edward Hart-Davis]

Just now, there was so much grief that the gchecks rolled over themselves, but there would have been plenty of useful data to go back through, and likely more bans to make, or more informed decisions to be made in the moment.

1000 simply isn't enough sometimes.

This is related to https://bitbucket.org/minecraftonline/scripts/issues/428/last-gcheck-number-command

[Anna Bakker]

This is a griefalert change, not a scripts one.