Standardize outputs of various bfast functions

[mirt001]

This is partially aesthetics, but also functionality. E.g. bfastpp return(rval) bfast return(structure(...)) bfastlite return(Result) bfastmonitor return(rval) # rval = list(...) bfastts return(ts(..))

It would be nice if the above would be standardized, e.g. returns could either return a variable that is suitable for the context, or a variable that is called e.g. result. Also, we have various structures for bfast bfastlite, but not for bfastmonitor. Not sure if they are all needed.