Charles McQuillan/Getty ImagesMichelle O’Neill was named Northern Ireland’s top government leader on Saturday in a historic appointment for her party that represents a sea change in Irish politics. O’Neill belongs to the Irish Republican Party Sinn Féin, which is historically associated with the Irish Republican Army (IRA) and favors unity with the rest of Ireland. Northern Ireland’s government has been long dominated by the Democratic Unionist Party (DUP), which prefers to keep Northern Ireland