Support natspec in contract/interface/library completions

[kanej]

Similar to #328, provide a subset of natspec auto-inserts on a /** */ completion before a contract or library or interface.

Based on the docs: https://docs.soliditylang.org/en/latest/natspec-format.html#tags, it looks like only @title, @author, @notice and @dev are supported. Lets include @title and @dev by default leaving @notice and @author out.