Update Bower's `main` to contain usable JS files.

I noticed the `main` property in `bower.json` is defined as [bootstrap.js](https://github.com/twbs/bootstrap-sass/blob/master/vendor/assets/javascripts/bootstrap.js), whose contents look like this:

```js
//= require bootstrap/affix
//= require bootstrap/alert
//= require bootstrap/button
//= require bootstrap/carousel
//= require bootstrap/collapse
//= require bootstrap/dropdown
//= require bootstrap/tab
//= require bootstrap/transition
//= require bootstrap/scrollspy
//= require bootstrap/modal
//= require bootstrap/tooltip
//= require bootstrap/popover
```

`main` is meant to define the file(s) which are usable by the consumer of your component. The file above isn't usable outside of the environment of this repository, so I simply added the individual files to the `main` array.

A better option may be to include the distributable version of `bootstrap.js`, such as the [bootstrap repo does](https://github.com/twbs/bootstrap/blob/master/bower.json#L18).