[config] Split stored string before use in add_list

ConfigParser.get() reads configurations (eg. channel list) as a string causing wrong lists to be stored back and/or calling <string>.append which also caused a crash

i.e. If you run "willie -w" more than once, the previous config is loaded as a string. When ','.join(lst) is called and the result stored, the config file now holds "#,l,i,n,u,x,,,#a,l,g,o,s"
Similarly, any attempt to append to this string will fail.

Solution: Split the string before use, converting it to a Python list.