New implementation of drag & drop (continued)

[PwtKCL]

In this PR, I've fixed a bug in the new implementation of the drag & drop that could cause frames to be moved in an illegal position.
It also contains the feature request of #257

[neilccbrown]

Looks fine to merge, so I will do so. What's the replacement for the draggable group logic? I was using that in the new OOP stuff but I guess I need to make a change in a different part of the code now (e.g. class frames should only allow comments and functions)?

[PwtKCL]

Looks fine to merge, so I will do so. What's the replacement for the draggable group logic? I was using that in the new OOP stuff but I guess I need to make a change in a different part of the code now (e.g. class frames should only allow comments and functions)?

There is no replacement as such. The groups were used as one layer for the checks of drag and drop - the other layer is a programmatic check against what frames are allowed at a given position. We can check together where in the code if needed;
Regarding the draggable group, there is no replacement because 1) the second layer of checking suffices and 2) if you see the commits of that PR, we seemed to only use the "all" group in the method I had deleted (...!).