Crawling strategy improvements and native logging

Here is the change log:

• latest SQLAlchemy unicode-related crashes are fixed,
• corporate website friendly canonical solver has been added.
• crawling strategy concept evolved: added ability to add to queue an arbitrary URL (with transparent state check), FrontierManager available on construction,
• strategy worker code was refactored,
• default state introduced for links generated during crawling strategy operation,
• got rid of Frontera logging in favor of Python native logging,
• logging system configuration by means of logging.config using file,
• partitions to instances can be assigned from command line now,
• improved test coverage from @Preetwinder.

Enjoy!