Handle context-free data

[tbfleming]

Change Description

Add support for context-free data in transactions. Signature providers may optionally support this. eosjs-jssig.ts supports it.

API Changes

• API Changes

Several functions and interfaces now have optional fields for handling context-free data.

Documentation Additions

• Documentation Additions

Overview of context-free actions and context-free data:

• Context-free data is an optional transaction field containing bytes[] (array of array of 8-bit values)
• Context-free actions in contracts may reference this data, but normal actions may not
• Context-free actions are similar to normal actions, but may not reference state. This includes, but is not limited to: tables, authorizations, current time, etc.
• ABI 1.0 and ABI 1.1 do not describe context-free data; it's opaque
• ABI 1.0 and ABI 1.1 do not distinguish between normal and context-free actions. It's up to users to know which is which, and place them in the appropriate transaction member (actions or context_free_actions)