Custom templates

The objective of this PR is to allow custom templates to be defined and remove any specific code related to the Twitter Bootstrap.

# New features

## Custom templates

Now it's possible to define in the wrapper the template name for inputs, labels, errors and hints. It can be defined globally (in the `default` wrapper) or for specific wrappers.

Example:
```javascript
Ember.EasyForm.Config.registerWrapper('default', {
  inputTemplate: 'inputForBootstrap'
});
```

## wrapperConfig

The `wrapperConfig` now is a computed property, so, it's accessible in templates and custom templates.

It's possible to define any value in the wrapper and use it in the template (or views).

Example:

```javascript
Ember.EasyForm.Config.registerWrapper('default', {
  someCustomClass: 'my-class'
});
```

```handlebars
<div {{bindAttr class="wrapperConfig.someCustomClass"}}>
my inputs
</div>
```


# Removed features

The options `wrapControls` and `controlsWrapperClass` were removed.

If the project uses the Bootstrap framework, it can define a custom template and the required config values.

# Documentation

I didn't update the documentation yet. I think it would be nice to have an example of how to define a custom template for Bootstrap.