re #829 take into account that higher_items may be in another sprint
board updater support for release backlogs
clarify higher_item method in activerecord_mixin
test for higher_item

reformat debug output of higher_item dump

elaborate list_with_gaps feature
use scope for higher_item: higher is what is seen visually on a backlog (sprint/productbl etc.), not next position
note problematic code regarding higher_item
tests: default to sprints project if not given in background table
when moving stories, use :next like the frontend does
remove up/down direction from story move tests
re #842 enable passing list_with_gaps tests
travis: drop 2.0, add list_with_gaps
use correct scope for higher/lower items, reorder find_options switch to become failsafe for scope, remove writer attr on higher/lower item which should be used only internally
refactor: break up complex find_options function
must not use order on options for list_commit
remove unused override of higher_item_scoped in rb_task
separate backlog queries to contain scope of higher/lower item virtual attribute
prove list_with_gaps move_before/after and optimize move_before by making explicit
elaborate confusing usage of prev and move_after when positioning a story
board-updater: take sharing into account
use scoped higher item in story view