[FIX] project_long_term: avoid bad duplication of phases

When we duplicate a project, the related phases need to be duplicated as well but keeping references between each other.
e.g. 'project 1' with 'phase A' follwed by 'phase B' should become 'project 1 (copy)' with 'phase A (copy)' followed by 'phase B (copy)'.
Fixing bug lp:1212860, opw 607062