Unit tests for issue 1136

This adds the basic unit tests for #1136.  The core problem appears to
be that we are tracking the repeated block edits as normal edits and not
a different command.  Hence it repeats as a simple edit instead of a
block edit.  Likely need a new InsertCommand for this to work
Removed dead code

Deleted some commented out code left over from a previous refactor
Implement block insert repeat

This implements the bulk of the work for issue #1136.  Block insert
repeat is now functional.  I still need to do some cleanup on the
implementation though.  But the functionality is there now
Cleaned up the code

This cleans up the code around block insert repeat.  It no longer uses
TextChange but instead a simple string value.  This is more
representative of what is legal for a block insert because TextChange
can mean delete or add while string shows just what is added

closes #1136
Merge pull request #1140 from jaredpar/fixes-1136

Fixes 1136