Jbrowse JBrowse

Can now grab and drag features to the annotation track to create annotation features without pre-selecting them--just
grab and go.
This is done by making features draggable on mouseover. I wanted to make this happen on mousedown (clicking on the
feature you want to drag), but that seemed to be too late already, so I had to do it on mouseover. It only happens
on the first mouseover of each feature, so it shouldn't cause much of a slowdown, but if it does turn out to be an
issue (e.g. when there are a lot of features loaded) I will revisit it.
https://github.com/GMOD/jbrowse/commit/0b50fc818d6acc5bfa739722c237...