script load path is harcoded

[terminaldweller]

Currently the load path for the python scripts is hardcoded to either be $(data_dir)/irssi/scripts or $IRSSI_HOME/scripts.
The module will refuse to load scripts from other paths.
The message returned in this case is a "script not found" which is not helpful and confusing(if you expect the same behaviour as the perl module).
Either the error message should reflect this or like the perl module, we should allow the python scripts to be loaded from other paths as well.