Improving nodejs.sh

- You can change the default Nodejs version
- Now you can use NVM in zsh as well.
- Uses custom nvm_install.sh @ https://gist.github.com/Ilyes512/8335484
- Global Node Modules/Packages as mentioned at #34 are now included within nodejs.sh
- Deleted yeoman.sh as it is unnecessary now

edit:

If ZSH is installed while installing NVM you will see the following errors:
```bash
/home/vagrant/.oh-my-zsh/oh-my-zsh.sh: line 13: syntax error near unexpected token `('
/home/vagrant/.oh-my-zsh/oh-my-zsh.sh: line 13: `for config_file ($ZSH/lib/*.zsh); do'
```

I don't know what/why, but everything still seem to work.