Add support for BinaryIntegerLiteral and OctalIntegerLiteral.

This fixes #1531.
It shares HexIntegerLiteral code for lexing BinaryIntegerLiteral and OctalIntegerLiteral.
Also, adds "isLegacy" property to ES5 OctalIntegerLiteral, to avoid triggering W115 warning for ES6 OctalIntegerLiteral.

@caitp I have this locally, so whenever you sign-off, I can land it.