admin-dashboard: add admin field in user model
admin-dashboard: admin user can edit boards
admin-dashboard: admin user and board owner can delete the board
admin-dashboard: vendors now belong to boards
admin-dashboard: admin can edit and delete vendors
admin-dashboard: admin can create or edit a vendor to belong to any board
admin-user: admin can edit and delete board reviews
admin-user: admin can edit and delete vendor reviews
Merge branch 'admin-dashboard'