Move extracting archives from source loader to plugin

[onionka]

I have a lot of reasons why this should be like this.

First of all our solution for extraction at this time is at the best temporary - this needs to be re-factored:

Nowadays there are many archive formats and they are so different that not even in python there is not a uniform way to extract archive. Our solution is heavily depended on system programs such as tar, bz and it is not working quiet well at this time.

So I think there should be new plugin phase - Extraction(self, archive, output_dir) that should extract archive to directory, if archive type matches. It will be extensible so we don't have to worry about implementing a lot of extraction algorithm.

[jsilhan]

could be a good idea. extraction(self, archive, output_dir) method should return boolean. It should be called on plugins in the loop until it gets return code True.

[onionka]

I think this should be high priority because if you want final api our lasting solution is only temporary and needs to be replaced ... For instance it didn't work on arch.tar - it is bugged and hard-coded.