Added pass-through of opts to MPSt::applygate.
Moved templated gateTEvol method to header to allow general template arguments (especially any type of container for the gates).
Fixed bug where scale factor wasn't included in eigs returned from ITensor svd.
Minor improvement to OptSet operator& overloads.
Changed signature of Observer methods to only accept an OptSet argument for maximum flexibility across use cases. Also Observer is no longer a pure virtual class so it can act as a do-nothing default. Removed some unused variables in eigensolver.h