Creating multi builds configs can be tedious. One must create 2 build
configs and 2 build config steps in the right order.
With this commit, a simple wizard is added that creates those 4
configurations by simply filling 4 fields.
Also, a new field, group, is added in order to be able to gather
config's and config steps into groups. The group is a Many2one on a
config.
While at it, the runbot menu has been a bit rearranged with everything
about config's in a parent menu named Configs.
Config's and config's steps tree views have been enhanced to show the
config group and add some filters in the search views.
