feat(lex,parse): Add stub try/catch implementation

[sjbarag]

Implementing try/catch/throw takes a good bit of work in the interpreter, so I'm splitting that into two pull requests. This one includes parsing try/catch/end try (without throw), and always executes only the try block to maintain backwards compatibility. It's a weird partial state, but the alternative is a massive pull request that can't be reasonably reviewed or understood.

see #554

[lvcabral]

Try..Catch and Throw implementation was finished in the Roku Community fork: https://github.com/rokucommunity/brs/releases/tag/v0.46.0