Pull Request: Twitter-In node topics on input, refresh interval input

[hgill]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Updates on Twitter-In node:

1. Node now takes topic string input rather than hard-coded
2. "Sticky" followers: If new input string suggests updates in handles to follow, creates "sticky" new intervals - meaning previously followed handles are maintained, new ones added
3. Node now takes refresh time as an input value, previously hardcoded at 60s

Other info:
4. I didn't add unit test cases, as I couldn't get the unit test lib to work as expected - can do with some guidance
5. I intended to use the latest Twitter API v2 which has breaking changes, but till v1.1 is functioning, thought it's best to let it be. When Twitter announces sunsetting of v1.1, I would like to contribute to upgrading this library to support v2.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality