internal/ui/jsonstatus and termstatus sound similar but are not related
in any way. Instead `internal/ui/backup` and `internal/ui/jsonstatus/status`
are the counterparts. Rename the latter to `internal/ui/json/backup` to
make this clear.
jsonstatus wrote the JSON output without synchronization to the
stdio_wrapper which caused mangling between different status lines.
Use the Print and Error methods of termstatus instead which use a
central goroutine to synchronize output.
