Add tests, fix config initialization issue, move/copy according to import config options, handle reimports

I have fixed an issue where the default print_ignored configuration value of 'no' was actually evaluating as true.

Additionally I have added some integration tests ensuring functionality during an import.  A copy of the beets source code needs to be available next to the copyartifacts directory for use by the tests. Executing "python tests/test_copyartifacts.py" from within the plugin directory will run the test suite.

The plugin now copies or moves depending on the import config settings.  Also reimporting now does not recopy the files and if the no copy option is used during an import, the files are not copied.

Config variables are read at runtime to allow easier testing of the configuration options.