Body-based phase calculator

[aandergr]

Instead of having to specify tuples of delta v, minimum acceleration and environment pressure, it should be possible to specify phases as "body.location-body.location" pairs where valid body values are: bop, dres, duna, eeloo, eve, gilly, ike, jool, kerbin, kerbol, laythe, minmus, moho, mun, pol, tylo, vall and locations are: intercept, orbit, soi, stationary, surface. e.g., a stage from Kerbin orbit to minmus surface would be kerbin.orbit-minmus.surface. The required constraints should then be automatically computed.

This feature would heavily enhance usability of kspalculator.

An implementation of this feature was started by @abaire, in commit edabc5e as well as its parents in phasecalculator branch.