Modify callSignature structure to hold active/output variables as vector of strings

[ImProta]

Currently we store the input and output variables as std::string in the callSignature class structure
Ideally we should read the yaml file and store the values as std::vector<std::string>
Examples:

functions:
active: x, a, b
output: z

_functions[0].active => "x, a, b"

Ideally:

_functions[0].active => ["x", "a", "b"]