Add conversation memory

[monarchwadia]

We need to add memory functions that allow the Ragged object to remember the context of the conversation.

By default, this feature should be off.

• startMemory() -> promise : enables memory
• stopMemory() -> promise : pauses memory collection. this does not clear memory.
• clearMemory() -> promise : clears the memory
• getMemory() -> promise : returns the memory
• setMemory(memory) -> promise : sets the memory

[monarchwadia]

We decided to let the dev manage memory themselves. Closing this as wontfix.