Support accessor set input

[averissimo]

Related issues

• Closes #43.

Changes description (include a screenshot if applicable!)

• Support accessor as well as an index in setInput
• Adds unit tests in R

Definition of Done checklist

• [x] :spiral_notepad: README, other documentation and code comments that we have is updated with all information related to the change.

• [x] Unit tests added for all new or changed logic.

• [ ] End-to-end tests added for all new or changed logic.

[averissimo]

I believe I resolved all your comments @kamilzyla

• [x] removed setInputUsage
• [x] updated webpack so that there's no hashing option to maintain
• [x] rename argIdx to jsAccessor
• [x] break triggerEvent to its own dataMapper called dataMappers.event

Please take a look at the changes I did to setInput as it seemed redundant to have code in R and JS handling the index vs. accessor

I'm a bit ashamed of the time it took to figure out a bug I was having with (...args) to arguments with webpack 😅

[averissimo]

I dropped the ball on the documentation. Thank you for catching it!