Custom toolbar by task in fof.xml

Because the view is pluralized ([See here](https://groups.google.com/forum/#!topic/frameworkonframework/IvSSW4KYWt4)), we can use only one toolbar for all the task in `fof.xml`. It makes this feature useless, we generaly need at least 2 toolbars (browse and edit).

So I make some change:
https://github.com/Eighke/fof/commit/d770538cb881621001acdc88288748ccf0b98fde

It allow to create toolbar per task:
```XML
<view name="items">
	<toolbar>
		<task name="*">
			<button type="unpublish">Unpublish</button>
		</task>
		<task name="browse">
			<button type="publish">Publish</button>
		</task>
	</toolbar>
</view>
```

I keep the current behavior for backward compatibiliy so it is still possible to use:
```XML
<view name="items">
	<toolbar>
		<button type="unpublish">Unpublish</button>
		<task name="browse">
			<button type="publish">Publish</button>
		</task>
	</toolbar>
</view>
```
So
```XML
<button type="unpublish">Unpublish</button>
```
is the same as
```XML
<task name="*">
	<button type="unpublish">Unpublish</button>
</task>
```

I'll create the doc if it looks good for you. :)