CLEANUP: cli: rename the last few "stats_" to "cli_"

CLEANUP: cli: rename the last few "stats_" to "cli_"

There were still a very small list of functions, variables and fields
called "stats_" while they were really purely CLI-centric. There's the
frontend called "stats_fe" in the global section, which instantiates a
"cli_applet" called "<CLI>" so it was renamed "cli_fe".

The "alloc_stats_fe" function cas renamed to "cli_alloc_fe" which also
better matches the naming convention of all cli-specific functions.

Finally the "stats_permission_denied_msg" used to return an error on
the CLI was renamed "cli_permission_denied_msg".

Now there's no more "stats_something" that designates the CLI.