BREAKING CHANGE: Removing the `ng init` & `ng update` commands because their current implementation causes more problems than it solves. Once RC is released, we won't need to use those to update anymore as the step will be as simple as installing the latest version of the CLI.
It requires little tweaking in the case-block.
Now the completion shell script is generated out of TypeScript code entirely. The options and aliases are generated dynamically. There are options to only produce bash- or zsh-specific code.
Closes#3981.