Write out profile information in open trace format OTF2

Suggested by Ed: There is an open trace format that is used by other profile visualization tools such as vampire and TAU. If DMRG++ can also write out trace (start/stop) information in this format (perhaps in a different file, not .cout), then other tools can be used. Open Trace Format OTF2 https://zenodo.org/record/1240852#.W7z9GS2lTOQ