SplitView doesn't handle dynamic remove of items

Since Qt 5.4.0 alpha the SplitView gained the ability of adding an item dynamically by using the "addItem" function. However the SplitView lack of a symmetric "removeItem" function.

Furthermore the API should be on par with the TabView one so the following functions should be added:

• insertAt(index, item)
• removeAt(index, item)