Add plot type "power" and Watt format.

Note that this technically breaks backwards compatibility of trace files
for 0.9.2 builds. But, whatever, as it's not yet released.

server/TracyTimelineItemPlot.cpp

@@ -38,6 +38,9 @@ const char* TimelineItemPlot::HeaderLabel() const
         }
     case PlotType::SysTime:
         return ICON_FA_GAUGE_HIGH " CPU usage";
+    case PlotType::Power:
+        sprintf( tmp, ICON_FA_BOLT " %s", m_worker.GetString( m_plot->name ) );
+        return tmp;
     default:
         assert( false );
         return nullptr;