[IMP-dev] Harmonic oddities

Now that I actually tried to use it, I find the Harmonic class a bit odd. For one thing the parameter is called "standard deviation" or something, which doesn't mean anything for a harmonic. Secondly, once you figure out what it is, it is multiplied by a many significant figure constant before it is used (the documentation says this is for modeller compatibility). This multiplier makes it very hard to use the Harmonic as part of a scoring function (since it is hard to make the composite function continuous).

Do we really want this? In my mind the thing that makes the most sense is to to have a the mean and the spring constant be the parameters and to get rid of the odd multiplier.