Few changes from my fork which you could review and merge.

The following is the summary of the changes made,

Fixed the bug where if you specify font-name without specifying font-size, the renderer would set the font-size to 0, hence the text would not be visible.

Add image-insets property to TabBar.
Add background-image-selected to TabBar's selectionIndicatorImage.

Add image-inset to TabBarItem.
Add finished-image and finished-image-selected to TabBarItem