Edit history: Option to migrate channels between communities

Current problem

Channels cannot be migrated from one community to another.

Proposed change

Similar to when certain channels were manually moved from Fluxer Developers to Fluxer Labs, it would be nice for someone that has admin privileges (or maybe only the owner?) in 2 communities to be able to move channels from one to the other. I'd expect the option to present itself when making a new channel, where the choices would become:

Text Channel
Announcement Channel
Voice Channel
Link Channel
Import

Perhaps an additional dialogue in Community settings that would allow for importing/migrating multiple channels at once, or to merge the communities altogether.

Additional information

Other consideration that come to mind:

With federation, channels would need to be capable of physically migrating between instances
Should users be migrated to the destination community by default? Regardless, should probably have a toggle
Non-optionally, the old location of the channel would be removed, since this is not meant to be an active mirror