Add mirror command, commands to mirror and rotate clipboard, cut command

[Firigion]

• mirror command to supplement the rotate command, so we can set a structure in any possible orientation.
• cut command to supplement move and copy (would be a shorthand for /se copy /se set air).
• mirrorc and rotatec commands to rotate and mirror clipboard, to mimic WE behavior of rotate
• add a flag to delete the selection after rotating or mirroring it. It's not the same as running /se set air after rotate or mirror because those commands might place blocks inside the selection. A workaround would be to copy/cut, rotate clipboard wnd then paste, but why do that when we can add more flags? I suggest maybe -r, for remove, but we are gonna run out of letters sooner than later.