test(sortable): add test for nested sortables where update is not firing
feat(sortable): add workaround for nested sortings not triggering update
test(sortable): add test for dragging items from parent list into nested list
Merge pull request #199 from thgreasi/nested

feat(sortable): add workaround for nested sortings not triggering update
feat(sortable): support helper functions returning an existing list element
chore: increase version number to v0.12.8
Merge pull request #200 from thgreasi/v0.12.8dev

chore: merge version v0.12.8 into master