add selection cut for Diboson event to master

Port the merge of branch 'diboson_selection_cut' into 'master'

See original merge request !672 (merged) to 'Sim09'

(cherry picked from commit ab2ec062)

• f5072115 Add selection cut for Diboson events
• f52bbd5a update DiBosonType according to Adam's comments
• 368c05cf Update DiBosonType.cpp. To fix m_motheroflepton bug.