user defined feature creation from a region selection

It should be possible to make the current selection into a set of features over the start/end positions of each of the selected sequences. Ideally, the user would use the pop-up region menu, or have some keystroke to do this. The interface should also allow the user to re-use the same feature name for multiple selection-feature creation steps, when marking up a large number of distinct regions on an alignment.

Note the relations between this request and the other feature feature requests (editing group and names of features, and deleting features).