Add a option `check_unique` in nodes.add #44
Merge branch 'v2.1' into check_unique

Conflicts:
	lib/dataprocessor/nodes.py
Merge branch 'validate_link_bug_fix' into check_unique
Change keyword "check_unique" > "strategy"
Add `check_duplicate`
Add tests
Merge branch 'v2.1' into check_unique
Merge branch 'v2.1'.
Update css.
Enable to sort with string order.
Merge branch 'enable-sort-by-string-order'
Enable to show or hide table item.
Bug fixed.
Merge branch 'master' into show-hide-table
Bug fixed.
Bug fixed.
Remove unnecessary files
Modify some descriptions
Update css.
Update looks of the selector.