Added C1 interpolants for plots. Adjusted other plots to be consistent.

Smoothing plot: forced 1/r to be 1000, using ylabel, and boxed key
Nesting plot (B-spline): using boxed key and default colors.
Nesting plot (C1): using boxed key and default colors.
main.cpp: includes phiC1.h, should be removed in the future.
Created polynomial theta and test function in gamma[.c|.h].

thetap is not so useful from 1 < x < 2, but I'll leave it in just in case
it may become useful in the future.