Add utility to get alpha insertion point in sub-menus

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Add a test for get_alphabetical_insert_position()

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Fix for case where new item should go at the end

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Passing test

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Tighter tests, better fix for condition when new item will sort to the end

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Add documentation

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Merge pull request #2556 from mkoistinen/toolbar-submenu-alpha-util

Add utility to get alpha insertion point in sub-menus