[WIP] Introduce views

- [x] Add view entities
- [x] Allows views entities inheritance
- [x] Update `CrudManager`
- [x] Update `dashboard`
- [x] Update list view
- [x] Update `Reference`, `ReferenceMany`
- [x] Update create / update view
- [x] Update ReferencedList view
- [x] Update deletion view
- [x] Update tests
- [x] Rebase
- [x] Update `sortParams`, `headers`, `validation / validator`, `filterParams`, ``
- [x] Update doc
- [x] Write migration doc
- [ ] Find a faster way to copy view

Example:
```js
var tag = new Entity('tags')
    .label('Tags')
    .order(3)
    .addView(new DashboardView('tag-dashboard')
        .order(1)
        .limit(10)
        .label('Recent tags')
        .addField(new Field('name').label('Name').type('string'))
        .addField(new Field('published').label('Published').type('boolean'))
    ).addView(new ListView('tags-list')
        .title('List of all tags')
        .pagination(pagination)
        .infinitePagination(false)
        .addAction(new Action('new-tag').label('Add tag').redirect('tags-create'))
        .addField(new Field('name').label('Name').type('string'))
        .addField(new Field('published').label('Published').type('boolean'))
        .addField(new Field('actions')
            .type('callback')
            .list(true)
            .label('Test')
            .isEditLink(false)
            .callback(function() {
                return '{{ entity.getField("name").value.toUpperCase() }}';
            })
        )
    ).addView(new FormView('tags-create')
        .addField(new Field('name')
            .label('Name')
            .type('string')
            .validation({
                "required": true,
                "max-length" : 150
            })
        )
        .addField(new Field('published').label('Published').type('boolean'))
    ).addView(new FormView('tags_edit')
        .addAction(new Action('delete-tag').label('Delete tag').redirect('tags-delete'))
        .listView('tags-list')
        .addField(new Field('name').label('Name').type('string').editable(false))
        .addField(new Field('published').label('Published').type('boolean'))
    ).addView(new DeleteView('tags-delete')
        .addField(new Field('name').label('Name').type('string').editable(false))
        .addField(new Field('published').label('Published').type('boolean'))
    );
```
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