Cleanup claims only from selected channels

[belikor]

This follows from the closed issue #6.

At the moment the generic function clean.cleanup_space looks at all claims. The parameter never_delete considers channels to avoid when deleting claims.

Maybe a new parameter only_delete could do the opposite, and consider only these channels when cleaning up older files.

channels = ["@lbry", "@odysee"]
dd = t.cleanup_space(main_dir="/opt", size=1000, percent=90,
                     only_delete=channels, what="media")

Internally, the function would use the methods clean.ch_cleanup and clean.ch_cleanup_multi introduced in e45bf17.

These functions delete all videos from a particular channel leaving only the newest one, established by the number=x parameter.