Create Swift Bitcoin Gold framework

[martin-key]

Create BTG framework on Swift to be used by Swift developers
Features:

• Connect and read data from insight explorer
• Read Block info
• Read TX info
• Create transaction
• Parse transactions
• Sign transactions
• Beam transactions
• Generate Private keys
• Check balance

The framework should support:

• Cocoapods
• Swift Package Manager
• Cartage (optional)

[martin-key]

@h4x3rotab proposed bounty:

• 75 BTG for entirely new framework
• 40 BTG for modified framework