Simplify catalog structure as stalbeton did

[duker33]

Their schema described at the comment https://github.com/fidals/stroyprombeton/issues/723#issuecomment-508773473

[duker33]

realized that structure refactoring is just throwing away Series and Sections. With not a huge logic redesign. But can throw them away only after taking data from stalbeton. What is required for stalbeton data taking is only Categories hierarchy with products structure. Maybe we'll throw away options.

So, i developed this global strategy of refreshing catalog:

• parse stalbeton
• merge it with the current catalog
• rewrite logic around Category-Product structure instead of (Category|Series|Sectoins)-Product-Options one