Gantt: do not ignore project filter (#7000, #7352), do not display empty projects/versions, and display shared versions used in other projects (#5817, #6476, #6604).
Related issues
Defect #5817: Shared versions not shown in subproject's gantt chart
Defect #6476: Subproject's issues are not shown in the subproject's gantt
Defect #6604: Issues targeted at parent project versions' are not shown on gantt chart
Defect #7000: Project filter not applied on versions in Gantt chart
Gantt: do not ignore project filter (#7000, #7352), do not display empty projects/versions, and display shared versions used in other projects (#5817, #6476, #6604).