Allow silencing of threads

[ChrisLovering]

Threads (& forum posts) can now be locked without the need to close them. This behaviour is exactly what we want for silencing a thread, and mods can still type in the threads without causing them to be unlocked.

We should update the Silence cog to allow for threads to be both silenced and unsilenced.

[MedAliMarz]

This look like a good issue to tackle, can i work on it ?

[shtlrs]

Sure, I've assigned you!

[wookie184]

@MedAliMarz Hi, did you make any progress on this?

[Snipy7374]

Hi, i woud like to work on this