Add reftrack window.

Add ui file and compiled ui file and a unfinished base window class.
Fix restriction check and scene suggestions without current element

Typo in is_restricted causes error. Also return no suggestions if there
is no current element.
Add set parent convenience function.

Removes child from old parent and adds to new.
Fix constructor of widget delegate views

The parent argument should be optional.
Add stub and implementations for most of the basic reftrackwin functions

Add all functions to make it functional. Some still raise NotImplementedError.

Insert filter checkboxes into own gridlayout.
Fix set taskfileinfo after replace

Also added test if taskfileinfo is correct after action.
Fix check selection for save for assets

Provide the release type argument.
Added plus icon to reftrackwin
Add get option labels method

Because the options of a reftrack can be an arbitrary treemodel
the option labels should describe what each level of the tree is.

E.g. first level are the tasks, second the descriptors and third level
the versions.
Add type color to reftrack

Update ReftrackItemData with new column type.
Foreground Color uses the new function.
Merge branch 'feature/JP-110-abstract-reftrack-gui' into dev