Tree View

Solves #41 (closed).

!297 (closed) Already exists pertaining to this, but this MR takes a different approach.

This MR creates a new ThunarStandardVeiwModel Interface which is to be implemented by all the view models i.e list-model, tree-view-model (part of this MR).

In !297 (closed) the list-model was internally modified. This lead to problems when changing views (from details-view to icon-view & vice-versa). Additionally ThunarPathEntry also uses list-model.

Also this change was made keeping in mind #14.

Tasks

• Create ThunarStandardViewModel
• Modify ThunarListModel to implement ThunarStandardViewModel.
• Create ThunarTreeViewModel
  • Implements ThunarStandardViewModel
  • Try running details-view with the newly created model.
• Modify ThunarStandardView to support changing of models when changing views.
• Keyboard navigation in tree-view.
• Toggle tree-view through view menu while in details-view.
• Added Thunar preference checkbox to always open details view in tree-view mode.
• Thunar Critical on switching file counts in configure columns dialog box.
• Create a UML diagram to showcase the hierarchy of the newly added models.
• Toggling show hidden option has no effect after the first call.
• Refactor code. (Naming, formatting, etc)
• Check for leaks.

TODO (after Merge)

• #1144 (closed) - Properly define and implement the drag and drop of expanded files.
• #1146 (closed) - Improve Thunar responsiveness (remove freezes) when opening 10000+ files.
  • Explore the various solutions. Make things more async.
  • Investigate the cause of the freeze.
• #1145 (closed) - XL & XL+ thumbnails.
• #1148 (closed) - Expanding folders in single click mode will activate them
• #1149 (closed) - Select files after action in list view
• #1156 (closed) - Reload is called once per subfolder

Note: Switching between views should work now.