True energy density for isolation corrections
This adds two decorations requested as a part of ATLASG-1511, describing the true energy density in the central and forward regions. They are used in lieu of adding further isolation decorations particularly for photons. The two decorations appear on the EventInfo.
FYI @jcatmore , @elmsheus , @tursom , @jcantero , @pilkingt , @emeoni , @jterron , @ancuetog , @llorente , @fsiegert