Add component.json for the Bower web package manager

This commit is a basic template of component.json for the Bower web package manager. Create by
```
bower init
```

If this pull request is accepted then register MathJax to [Bower's registry](http://sindresorhus.com/bower-components/)
```
bower register MathJax git://github.com/mathjax/MathJax.git
```

Once registered to Bower, developers can download MathJax via
```
bower install MathJax
```