[WIP] add usage widget

This Pull Request is a test to get a usage wizard /widget in Contao.
It is still under progress. So feel free to share ;)

I am not sure if it works, but it makes me crazy that I am not know on wich pages my layout is used wich I currently edit ;).

So it works pretty well. You have to copy the `core-uncompressed.js` into `core.js`.

I am not happy about the button underneath the widget `Auswahl ändern`. So we can discuss about this and all the other stuff ;)


### Todo (I will update it if I miss something in here ;))
- [x] Usage Wizard for Layouts
- [ ] Usage Wizard for Moduls
- [ ] Usage Wizard for Files -> This is dificult because there is this tinyMCE. For me it is no problem, because I removed the options to add Images in the tinyMCE. ;) So all thos images wich are added in the are missing ;)
- [ ] Think about insert Tags... `{{insert_module::*}}` `{{image::*}}` Not sure how to handle this.

### Please Notice:
The core widgets normaly have lots of inline HTML and so on. I hat this. because of that ther is an extra `be_usage_widget.html5`. If this is OK so tell me, and I will rework all the other widgets! ;)

So I have read the mails from @leofeyer to not chage the syntax and have the same structure on similar code... But I can't do it like this way. Sorry for that.

### Commit Notes:
initial commit for usage widgets
- added reloadWidget to Ajax.php
- added template be_usage_wizard.html5
- added usage wizard JavaScript for reloading the widget
- added usage widget to the layout
- added UsageWizard.php to the config and autoloader