Making auto-correction off by default

- Allows for the user to turn on auto-correction using the
$ENABLE_CORRECTION variable
- Adds aliases regardless of variable assignment to aid users that use
setopt to turn correction back on in their zshrc
Cancel update if the current user doesn't have write permissions for the oh-my-zsh directory.
Revert "Cancel update if the current user doesn't have write permissions for the oh-my-zsh directory."

This reverts commit 152e1e07e0397ecc3f1778ea597d081c33ee8ff4.