[Feature] default value for filext_fnc_get

[m1kesk]

Current implementation of get is
private _name = [_fileName, "Name"] call filext_fnc_get;
in case there is no value, it returns nil.

suggestion:
Add third parameter default value in case get function don't find it in file.
example:
private _name = [_fileName, "Name", "Unknown" ] call filext_fnc_get; // return "Unknown"