Create UX concept for supporting multiple Qt versions

To support loading and unloading kits dynamically we need UI component. This can be done within the normal settings as plugin.

The UI needs to be used when Qt DS is installed however, to ask from the user what kits they want to use.

Qt DS needs to load the JSON for kits from the server so it can show what is available.

When Qt DS is doing 'kit management' like loading or unpacking, it should show a progress bar indicator with cancel option.