Implement Tree package

[adrolli]

• Copy Tree package from web
• Namespace and composer moox/tree
• Test installation of package
• Test implementation in app scope
• Move implementation to Category package
• Move implementation to Base, if applicable
• Document implementation an test for Page, Post, Product ...

[adrolli]

Current state:

• nothing left in App scope
• package moox Category provides two plugins: Category and CategoryTree

[adrolli]

We need to know what we want.

So we need to explore, what is possible and what is missing:

• What features (draggable, nested) are available in the resource's table view?
• Would it be possible to use the table view of the resource instead of building an own?

Need features for the tree view:

• Translations - Language Switcher
• Search and Filter
• Bulk Actions
• New Category top right (default)

So, can we stick to the original view (header action, using table features)?