MainFrm: fast exit play command while opening
MainFrm: don't paint m_pCAP until the rect is set
MainFrm: don't pause the graph in graph thread

Interface repainting may be sluggish after it, instead, enter play or
paused state from main thread after everything is repainted
MainFrm: set icon before constructing the graph
MainFrm: add new MLS_FAILING load state
MainFrm: use strongly-typed enum for load states