remove phase and refactor motion close_at

fixes #569

Conflicts:

	spec/models/user_spec.rb

update schema
Merge branches 'master' and 'refactor/remove-phase-and-fix-close-date-issue' of github.com:loomio/loomio into refactor/remove-phase-and-fix-close-date-issue

* 'master' of github.com:loomio/loomio:

* 'refactor/remove-phase-and-fix-close-date-issue' of github.com:loomio/loomio:
  remove phase and refactor motion close_at