Python3 comes with a built-in readline module. It wasn't included up until
now; mostly because it wasn't considered.

This change introduces it as a sub-package of the main Python3 package.
readline support is included in Python.

libreadline pulls libncursesw as a package, so python3-ncurses was
updated to pull libncursesw as well.
It should be the same package; mostly done for consistency.

Resolves the issue reported here:
  https://forum.openwrt.org/t/python3-repl-missing-readline/90039

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>