Added rollup config to tests

[ncave]

• added Rollup config to Tests, seems to work.
• added Rollup config to REPL, seems to work.
• added a check cmd to try the new --checkJs option in typescript 2.3
  cd src/tests / npm run fable / npm run rollup / npm run test / npm run check

[alfonsogarciacaro]

Thanks!

[ncave]

@alfonsogarciacaro Thanks for merging.
I've briefly looked at the result of type-checking the Fable output with typescript 2.3 --checkJs option:
cd src/tests / npm run fable / npm run rollup / npm run test / npm run check (ignore the error)
I don't see any major issues that need fixing, but still it looks like a valuable tool for validating the Fable output without having to go the TypeScript AST way.