This makes the tag movement consistent to how it behave with cloning/adding frames.
in short tag behavior when moving frames from [A, B, C, ...] to [G, H, I, ...] will be the same as if: frames at indices [A, B, C, ...] is removed and new frames at [G, H, I, ...] is created
Note that the behavior at tag edges is a little different for the sake of making it more intuitive

It works like follows:

• If the entire tag is selected, then the tag moves as a whole (WITH the frames), if not then the frames are taken away from the tag and it's size decreases.
• The if frames are moved from point A to point B, the tags between these points move to the right
• The frames dropped inside the tag increases the size of the tag. (the boundary of the tag is not part of the tag)

I don't think anything got broken but testing is appreciated nonetheless