Added mdp option 'calc-lambda-neighbors'.

Added mdp option 'calc-lambda-neighbors'.

Added an option 'calc-lambda-neighbors' to limit the number of free
energy delta H evaluations and output operations: this value sets the
amount of neighboring lambda points to calculate and print the energy
for. If it's 1, it will only calculate directly adjacent lambda points'
energies (if it's -1, it will calculate all points). This tremendously
cuts down the number of (expensive) energy calculations done without
impacting the results for most users

Note that this commit only limits the number of outputs, not the number
of calculations. That is left for a later commit.

Change-Id: I10590dd1a2036b529946da86b414c2561d14bda1