refactor to boilerplate for other web-sites

[iAnanich]

Step 1 (v0.6+): completed

• refactor settings system
• keep scraping only unique articles even from different web-sites

Step 2 (v0.7+): completed

• fix gismeteo spider to scrape URL from promoted article
• spider inheriting

Step 3 (v0.8+):

• add video/photo extractors
• add scripts for automatically creating new worksheets

[iAnanich]

Already have spiders for other web-sites: feat/new_spiders