Add button rule

From https://discuss.tryton.org/t/required-clicks-per-button/222

assigned to @ced

added trytond type::feature + 1 deleted label

New review26791002 at https://codereview.tryton.org/26791002/#ps1

review26791002 updated at https://codereview.tryton.org/26791002/#ps20001

New review29631002 at https://codereview.tryton.org/29631002/#ps1

review26791002 updated at https://codereview.tryton.org/26791002/#ps40001

review26791002 updated at https://codereview.tryton.org/26791002/#ps60001

For me, it is ready to be tested.

added 1 deleted label and removed 1 deleted label

review28911002 updated at https://codereview.tryton.org/28911002/#ps1

review29631002 updated at https://codereview.tryton.org/29631002/#ps20001

review26791002 updated at https://codereview.tryton.org/26791002/#ps80001

review26791002 updated at https://codereview.tryton.org/26791002/#ps100001

Tested in gtk client during Tub2016 to force approval with 2 users. Working. (and the reset click too)

New changeset 48ca7078f8ca by C?dric Krier in branch 'default':
Add button rule
http://hg.tryton.org/trytond/rev/48ca7078f8ca

added 1 deleted label and removed 1 deleted label

closed

New changeset 0f405dcad099 by C?dric Krier in branch 'default':
Add support for button rule
http://hg.tryton.org/tryton/rev/0f405dcad099

New changeset cbe09211aed2 by C?dric Krier in branch 'default':
Add support for button rule
http://hg.tryton.org/sao/rev/cbe09211aed2