Added support for updating stages on versioned extensions managed through GridFieldSortableRows (ref #77)

Added standard .gitattributes file

Added standard .editorconfig file

Fixed regression introduced in fae85f04 where disableSelection() was no longer optional

Disable selection is now forced when the "allow drag and drop" is checked

Fixed issue where if there are no pagination arrows from GridFieldPaginator the arrows for sortable gridfield would show when dragging

Re-enabled removal code if the page sort does not have a previous and/or
next

Spacing corrections

Fixed issue where the even/odd highlight would differ from what the server would generate after sorting

Allow installation anywhere by adding yml config

Allow 'disableSelection' to be disabled

Resets the classes of .odd, .even, .first and .last for gridfields when a update (drop) event occurs.