CLEANUP: map/cli: take the "show map" context definition out of the appctx

CLEANUP: map/cli: take the "show map" context definition out of the appctx

This makes use of the generic command context allocation so that the
appctx doesn't have to declare a specific one anymore. The context is
created during parsing. Many commands, including pure parsers, use this
context but that's not a problem as it's designed to be used this way.
Due to this, many lines are changed but that's in fact a replacement of
"appctx->ctx.map" with "ctx->". Note that the code also uses st2 which
deserves being addressed in separate commit.