NNBD and Code Cleanup

[SupposedlySam]

Non Nullable By Default (NNBD)

• Update all optional parameters without defaults to be nullable by adding a ? to the end of the Type
• Update all values that can be null with a ? at the end of the Type
• Force non-null where needed with ! at the end of the Type
• Remove assertions now accomplished by the compiler and NNBD

Cleanup

• Convert all Map() to map literals {}
• Remove new keyword in lib directory