Give bgsubtract some bsxfun love

--CAR
Set the offset start point to the end value

Gives better fitting result when we don't fully recover.
Big clean-up of 2D ramsey fitting

Use KT guesses and work with new data ordering.
Fix awg amplitude sweeping string mismatch

Also add error catching.
Set the source frequency to the latest GUI frequency.

--CAR
Merge branch 'develop' of github.com:BBN-Q/Qlab into develop