[packages] Split out language package installs.

These can now be run independently of the rest of the install if
required.

This still needs some more work to simplify and give the user some
control over what gets done.
[install] Ask to install interpreter packages.

This will now ask the user prior to installing packages for Python,
Ruby, and Node.js.
[packages] Simplify interpreter package scripts.

This simplifies the logic in these scripts since now they can exit when
they cannot install.