Warn analyst of overlapping legs

[IanMayo]

A secondary track can be built up from a series of TMA legs.

It is possible to create legs that overlap in time. This can cause an issue in Debrief (#5152), but that should be fixed to allow them to overlap (including, for instance, if the contact is held on multiple ownship sensors).

But, some Debrief operations can't happen to a track with overlapping legs. One is generating infills and the other is merge legs. For both of these the operation can't be performed for overlapping legs.

So, when the analyst tries to do either of these, a dialog should popup which names the overlapping legs. The analyst can then choose to trim the legs in way that suits the data (such as favouring one sensor over another).