Show Theory Components

[Andreas Suter]

add PLOT block option which allows to show the various components of a multi-component fit. To be more specific: show theory function components which are separated by a '+', e.g.

a 1 se 2 tf map1 fun1 + a 3 se 3 tf map1 fun2

would show the full theory function and, in addition, the two TF parts.