Visualise storage slot values

[naddison36]

• Option to add storage slot values that are fetched from the chain to storage diagrams
• Unallocated bytes now shown in storage diagrams
• fix storage diagrams when the first variable uses multiple slots
• fix: imports of @ packages when using Etherscan to get source files
• Refactored storageObjects to storages and storage to variable
• Simplified default filenames
• bumped version to 2.1.0

Breaking changes from 2.0.x

• renamed the --contractName <value> option to just --contract <name>