Fix permission settings for QOTW submissions channel in QOTW jobs

[Defective4]

JavaBot is meant to revoke users' permissions to send messages in threads in QOTW submissions channel after the QOTW submission period ends.
Currently after the submission period ends the bot resets all of the channel's role overrides for @everyone and doesn't deny the MESSAGE_SEND (and other) permissions until the next submission period starts, meaning that all members are allowed to send messages in the submissions channel during that short window of time.
Also since the bot resets the channel permissions at the start and end of submission period and does NOT set other permissions such as CREATE_PRIVATE_THREADS and MESSAGE_ADD_REACTION, all members are allowed to create new threads manually and add message reactions at all times.
This pull request fixes both of these issues by ensuring that MESSAGE_SEND permission is set to denied at the end of the submission period, and by denying the following permissions at both start and end of the period:

• CREATE_PRIVATE_THREADS
• CREATE_PUBLIC_THREADS
• MESSAGE_ADD_REACTION

[danthe1st]

LGTM and it works in my tests.