disable locked editing to allow user to insert gaps into a selected region to expand the selection

It is currently impossible for jalview to distinguish between the situation where the user has selected all columns in a row of an alignment, and wishes to insert gaps to expand that row, and when the user selects a region spanning the width of the alignment and wishes to perform locked editing.

As a result, selecting a sequence ID in the example alignment, and attempting to insert a number of gaps will fail because the selected region is not expanded as gaps are inserted.

A new key/edit combination or toggle mode is needed to allow the selected area to be expanded as gaps are inserted.