make FEP schedules configurable on a per solvent basis

[orbeckst]

Requires #1 to be implemented.

Note that at the moment the default for schedules in Goct are never used because we always pass the schedule kwarg in run.fep_simulation, which is taken from the input cfg file.

[ianmkenney]

@orbeckst Is this to say that if no values are provided in the configuration file, we are to use the defaults in the Goct subclass?

[orbeckst]

Yes, we should have some defaults and the Goct ones are as good as any (at least they work for octanol).

I would just call them "non-water solvent" defaults and it would be good to have them explicit in the config file somewhere.

Or perhaps better: Raise an error if no solvent parameters are given and we ship config files with explicit FEP schedules for water, octanol and cyclohexane.