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.