Sigma SDK v5.0.15 for Ergo mainnet v5.0.x

What's Changed

• unused code removed (#957, #961)
• predefined ErgoScript bigInt predefined function to create big integer fromString (e.g. bigInt("5")): #967
• JavaScript serialization and deserialization of Box in registers: #971
• Correct environment for Template Compiler: #977
• Simplify IRContext: #986
• Update flatMap documentation for Interpreter V2/Ergo 5.0: #954
• Parse ContractTemplate from JSON string: #999
• Check BigInt size on serialization: #996
• Add missing JavaScript reflection metadata: #1009
• Finish executeFromVar: #976
• Update Scrypto dependency #1036

Full Changelog: v5.0.14...v5.0.15