Hide empty cell in responsive tree view

For example when a button is not visible, it is useless to take space for it in responsive mode as all widgets position vertically.

assigned to @ced

added sao type::feature + 1 deleted label

added 1 deleted label and removed 1 deleted label

review278041002 updated at https://codereview.tryton.org/278041002/#ps282311002

review278041002 updated at https://codereview.tryton.org/278041002/#ps282421002

New changeset a1c89cb3c2b9 by Cédric Krier in branch 'default':
Do not display empty cell nor button label in responsive tree
https://hg.tryton.org/sao/rev/a1c89cb3c2b9

added 1 deleted label and removed 1 deleted label

closed

New changeset c8b0e89e7909 by Cédric Krier in branch 'default':
Do not display empty cell nor button label in responsive tree
https://hg.tryton.org/tryton-env/rev/c8b0e89e7909

mentioned in issue #8919 (closed)