Merge voTreeDropTip and voTreeDropTipWithData

[XiaoxiaoLiu]

There are some shared functions between voTreeDropTip and voTreeDropTipWithData right now.
This is a quick but dirty solution in order to make the drop tip operation work on both a single tree or a tree with table. For each analysis, the number of inputs is fixed so there is no easy solution to provide a single DropTip analysis for both input situations. We should move some of the shared functions to a separate file though to ease the future maintenance.