Implement FilterComboBox

• Added a new QComboBox subclass that represents the FilterComboBox
• Property 'filters' was created in UIFilterManager
• Filters loaded just one time
• FilterComboBox loads items through the filters property

Implement Documents Tree Widget to FilterManager

• QTreeWidget subclass 'DocumentTreeWidget' created
• It was added a new 'documents' property to UIFilterManager
• DocumentTreeWidget shows all documents(just first level for now)
• DocumentTreeWidget shows FilePath, Type(Document) and thumbnail(30x30)

Added new QTreeWidgetItem subclass to components directory

Support to Python/SIP objects into QTreeWidgetItem data

Implement Model-View pattern to build tree structure and show documents data

• I implemented a TreeItem class that represents each row in the tree
• Read-only QAbstractItemModel subclass implemented
• Adjusts in UIFilterManager

Implement First Level of the TreeModel

• QTreeView shows fileName (Documents), type and thumbnail.
• TreeItem stores the rootNode of each document.
• We can access Row data(Node) through Qt.UserRole + 1 (I will implement enums yet).
• MultiSelectionMode to QTreeView.
• I renamed some object variables to don't conflict with properties of the Model-View implementation.

Implement recursive loading of the Documents Tree View

• Invalid components removed (Items based)
• Method to load the first level of the tree was implemented
• Recursive method that loads all sub-level nodes from a root node was implemented
• UIFilterManager's layout updated to adjust contents to QDialog size
• Filter needs the document width and height to be applied
• It needs refactoring!!

Improve performance of the filter applier, saving document index in each node

• Using enumerate while iterating over document's list, I saved the document index, then it's propagated throughout tree(document's children)
• Confirm button implementation with apply method
• I need to fix a bug in the apply method from Filter class (libkis), for some reason, it's not updating the image in the canvas.

Fixes T5885

Ref T1625

I didn't implement a refresh button, so you need to open document(s) before the Filter Manager plugin. You can select any filter from the list and a set of nodes from any
document and apply it. I need to fix a bug in the apply method from libkis that is not updating canvas image.