In favor of simpler, hard-coded, list of sources, to avoid unneccesary magic.
Also: check to see if query has results before instantiating the meta sources
- `sync_data` -> `sync_from_source`
- properly catch ConfigValueError
- avoiding iterating through library if we couldn't instantiate any meta sources
- fix create_temporary_copy to actually make a tempdir
- MetaSources get loaded from the modules automatically
- The MetaSources can define their own item_types, that get loaded for the plugin
- __init__ doesn't need any changes to accept new metasources
- Fix the --sources option to actually accept sources
(it was being interpreted as boolean flag before, crashing the plugin)
- More safety w.r.t. external dependencies
- allows for the logging to integrate better
- renamed `get_data` to `sync_data`, to better reflect that its not returning anything,
but that the item's data is being set by the function
