Updates to Predicate Design and Addition of Bitcoin Scopes

[natebuch]

Description

Changes: Update predicate design documentation.

• There was repeated information between the Stacks and Bitcoin predicate page. Combined the documentation into a single page for better continuity.
• Updated predicate-design file
• Deleted bitcoin predicates file
• Deleted stacks predicates file

Add Bitcoin scopes reference file.

• Created reference page for Bitcoin scopes
• Nested Stacks and Bitcoin references pages under a scopes file

Reference Links

• Updated existing guides to point to new predicate design page.
• Updated existing guides to point to Bitcoin scopes, Stacks scopes or both based on context.